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 $62.42   8.177%   $67.5241   $67.52   $67.50   $67.50  
  Purchase #2 $205.69   7.773%   $221.6783   $221.68   $221.70   $221.70  
  Purchase #3 $148.63   4.270%   $154.9765   $154.98   $155.00   $155.00  
  Purchase #4 $194.95   9.803%   $214.0609   $214.06   $214.05   $214.10  
  Purchase #5 $116.51   9.579%   $127.6705   $127.67   $127.65   $127.70  
  Purchase #6 $45.77   5.195%   $48.1478   $48.15   $48.15   $48.10  
  Purchase #7 $47.43   4.307%   $49.4728   $49.47   $49.45   $49.50  
  7 purchase totals = $821.40       $883.5309   $883.53   $883.50   $883.60