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 $87.26   10.398%   $96.3333   $96.33   $96.35   $96.30  
  Purchase #2 $116.53   6.732%   $124.3748   $124.37   $124.35   $124.40  
  Purchase #3 $58.50   6.419%   $62.2551   $62.26   $62.25   $62.30  
  Purchase #4 $65.59   6.717%   $69.9957   $70.00   $70.00   $70.00  
  Purchase #5 $201.39   12.480%   $226.5235   $226.52   $226.50   $226.50  
  Purchase #6 $10.31   5.138%   $10.8397   $10.84   $10.85   $10.80  
  Purchase #7 $110.38   9.202%   $120.5372   $120.54   $120.55   $120.50  
  7 purchase totals = $649.96       $710.8593   $710.86   $710.85   $710.80