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 $226.93   13.202%   $256.8893   $256.89   $256.90   $256.90  
  Purchase #2 $240.51   10.719%   $266.2903   $266.29   $266.30   $266.30  
  Purchase #3 $115.34   4.416%   $120.4334   $120.43   $120.45   $120.40  
  Purchase #4 $72.83   9.303%   $79.6054   $79.61   $79.60   $79.60  
  Purchase #5 $10.48   9.351%   $11.46   $11.46   $11.45   $11.50  
  Purchase #6 $88.26   10.496%   $97.5238   $97.52   $97.50   $97.50  
  Purchase #7 $60.57   4.309%   $63.18   $63.18   $63.20   $63.20  
  7 purchase totals = $814.92       $895.3822   $895.38   $895.40   $895.40