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 $184.93   8.338%   $200.3495   $200.35   $200.35   $200.30  
  Purchase #2 $229.33   12.452%   $257.8862   $257.89   $257.90   $257.90  
  Purchase #3 $16.52   3.325%   $17.0693   $17.07   $17.05   $17.10  
  Purchase #4 $247.97   3.746%   $257.259   $257.26   $257.25   $257.30  
  Purchase #5 $119.65   6.705%   $127.6725   $127.67   $127.65   $127.70  
  Purchase #6 $61.43   5.122%   $64.5764   $64.58   $64.60   $64.60  
  Purchase #7 $18.28   5.812%   $19.3424   $19.34   $19.35   $19.30  
  7 purchase totals = $878.11       $944.1553   $944.16   $944.15   $944.20