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 $106.41   6.244%   $113.0542   $113.05   $113.05   $113.10  
  Purchase #2 $98.73   13.727%   $112.2827   $112.28   $112.30   $112.30  
  Purchase #3 $227.44   13.438%   $258.0034   $258.00   $258.00   $258.00  
  Purchase #4 $217.46   9.356%   $237.8056   $237.81   $237.80   $237.80  
  Purchase #5 $41.77   6.172%   $44.348   $44.35   $44.35   $44.30  
  Purchase #6 $223.85   4.458%   $233.8292   $233.83   $233.85   $233.80  
  Purchase #7 $221.81   5.348%   $233.6724   $233.67   $233.65   $233.70  
  7 purchase totals = $1,137.47       $1,232.9955   $1,232.99   $1,233.00   $1,233.00