Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.66   10.593%   $168.8313   $168.83   $168.85   $168.80  
  Purchase #2 $136.93   10.591%   $151.4323   $151.43   $151.45   $151.40  
  Purchase #3 $168.64   7.169%   $180.7298   $180.73   $180.75   $180.70  
  Purchase #4 $97.83   12.799%   $110.3513   $110.35   $110.35   $110.40  
  Purchase #5 $230.73   4.486%   $241.0805   $241.08   $241.10   $241.10  
  Purchase #6 $102.51   12.177%   $114.9926   $114.99   $115.00   $115.00  
  Purchase #7 $171.58   10.622%   $189.8052   $189.81   $189.80   $189.80  
  7 purchase totals = $1,060.88       $1,157.2230   $1,157.22   $1,157.30   $1,157.20