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 $88.91   9.273%   $97.1546   $97.15   $97.15   $97.20  
  Purchase #2 $8.88   13.655%   $10.0926   $10.09   $10.10   $10.10  
  Purchase #3 $124.42   11.191%   $138.3438   $138.34   $138.35   $138.30  
  Purchase #4 $60.74   8.566%   $65.943   $65.94   $65.95   $65.90  
  Purchase #5 $194.40   5.590%   $205.267   $205.27   $205.25   $205.30  
  Purchase #6 $55.77   9.385%   $61.004   $61.00   $61.00   $61.00  
  Purchase #7 $197.82   12.195%   $221.9441   $221.94   $221.95   $221.90  
  7 purchase totals = $730.94       $799.7491   $799.73   $799.75   $799.70