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 $203.25   10.167%   $223.9144   $223.91   $223.90   $223.90  
  Purchase #2 $103.40   10.830%   $114.5982   $114.60   $114.60   $114.60  
  Purchase #3 $45.26   12.130%   $50.75   $50.75   $50.75   $50.80  
  Purchase #4 $199.30   4.150%   $207.571   $207.57   $207.55   $207.60  
  Purchase #5 $238.76   8.365%   $258.7323   $258.73   $258.75   $258.70  
  Purchase #6 $123.73   13.690%   $140.6686   $140.67   $140.65   $140.70  
  Purchase #7 $214.36   8.360%   $232.2805   $232.28   $232.30   $232.30  
  7 purchase totals = $1,128.06       $1,228.5150   $1,228.51   $1,228.50   $1,228.60