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 $86.66   8.154%   $93.7263   $93.73   $93.75   $93.70  
  Purchase #2 $164.59   3.154%   $169.7812   $169.78   $169.80   $169.80  
  Purchase #3 $190.32   4.669%   $199.206   $199.21   $199.20   $199.20  
  Purchase #4 $93.85   8.354%   $101.6902   $101.69   $101.70   $101.70  
  Purchase #5 $146.93   5.846%   $155.5195   $155.52   $155.50   $155.50  
  Purchase #6 $20.51   11.623%   $22.8939   $22.89   $22.90   $22.90  
  Purchase #7 $205.41   6.153%   $218.0489   $218.05   $218.05   $218.00  
  7 purchase totals = $908.27       $960.8660   $960.87   $960.90   $960.80