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 $144.98   8.692%   $157.5817   $157.58   $157.60   $157.60  
  Purchase #2 $8.38   5.784%   $8.8647   $8.86   $8.85   $8.90  
  Purchase #3 $115.28   12.718%   $129.9413   $129.94   $129.95   $129.90  
  Purchase #4 $177.83   6.305%   $189.0422   $189.04   $189.05   $189.00  
  Purchase #5 $25.45   12.853%   $28.7211   $28.72   $28.70   $28.70  
  Purchase #6 $164.38   3.396%   $169.9623   $169.96   $169.95   $170.00  
  Purchase #7 $30.68   11.445%   $34.1913   $34.19   $34.20   $34.20  
  7 purchase totals = $666.98       $718.3046   $718.29   $718.30   $718.30