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 $43.99   12.456%   $49.4694   $49.47   $49.45   $49.50  
  Purchase #2 $204.96   8.792%   $222.9801   $222.98   $223.00   $223.00  
  Purchase #3 $163.89   3.670%   $169.9048   $169.90   $169.90   $169.90  
  Purchase #4 $240.25   8.497%   $260.664   $260.66   $260.65   $260.70  
  Purchase #5 $22.93   13.323%   $25.985   $25.99   $26.00   $26.00  
  Purchase #6 $111.42   13.717%   $126.7035   $126.70   $126.70   $126.70  
  Purchase #7 $88.98   12.638%   $100.2253   $100.23   $100.25   $100.20  
  7 purchase totals = $876.42       $955.9321   $955.93   $955.95   $956.00