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 $85.71   11.168%   $95.2821   $95.28   $95.30   $95.30  
  Purchase #2 $68.31   13.238%   $77.3529   $77.35   $77.35   $77.40  
  Purchase #3 $39.78   12.295%   $44.671   $44.67   $44.65   $44.70  
  Purchase #4 $185.78   8.485%   $201.5434   $201.54   $201.55   $201.50  
  Purchase #5 $45.92   9.687%   $50.3683   $50.37   $50.35   $50.40  
  Purchase #6 $206.91   3.218%   $213.5684   $213.57   $213.55   $213.60  
  Purchase #7 $99.74   11.729%   $111.4385   $111.44   $111.45   $111.40  
  7 purchase totals = $732.15       $794.2246   $794.22   $794.20   $794.30