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 $203.86   8.738%   $221.6733   $221.67   $221.65   $221.70  
  Purchase #2 $82.41   9.352%   $90.117   $90.12   $90.10   $90.10  
  Purchase #3 $31.32   9.766%   $34.3787   $34.38   $34.40   $34.40  
  Purchase #4 $24.48   4.658%   $25.6203   $25.62   $25.60   $25.60  
  Purchase #5 $102.67   11.310%   $114.282   $114.28   $114.30   $114.30  
  Purchase #6 $118.38   5.756%   $125.194   $125.19   $125.20   $125.20  
  Purchase #7 $171.89   10.143%   $189.3248   $189.32   $189.30   $189.30  
  7 purchase totals = $735.01       $800.5901   $800.58   $800.55   $800.60