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 $211.32   12.533%   $237.8047   $237.80   $237.80   $237.80  
  Purchase #2 $60.52   6.814%   $64.6438   $64.64   $64.65   $64.60  
  Purchase #3 $150.36   12.552%   $169.2332   $169.23   $169.25   $169.20  
  Purchase #4 $126.35   12.867%   $142.6075   $142.61   $142.60   $142.60  
  Purchase #5 $159.57   4.760%   $167.1655   $167.17   $167.15   $167.20  
  Purchase #6 $59.64   9.212%   $65.134   $65.13   $65.15   $65.10  
  Purchase #7 $229.25   8.856%   $249.5524   $249.55   $249.55   $249.60  
  7 purchase totals = $997.01       $1,096.1411   $1,096.13   $1,096.15   $1,096.10