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 $235.83   13.436%   $267.5161   $267.52   $267.50   $267.50  
  Purchase #2 $61.42   7.863%   $66.2495   $66.25   $66.25   $66.20  
  Purchase #3 $108.32   6.500%   $115.3608   $115.36   $115.35   $115.40  
  Purchase #4 $172.28   4.426%   $179.9051   $179.91   $179.90   $179.90  
  Purchase #5 $89.71   4.529%   $93.773   $93.77   $93.75   $93.80  
  Purchase #6 $170.86   8.443%   $185.2857   $185.29   $185.30   $185.30  
  Purchase #7 $32.97   8.483%   $35.7668   $35.77   $35.75   $35.80  
  7 purchase totals = $871.39       $943.8570   $943.87   $943.80   $943.90