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 $60.36   5.582%   $63.7293   $63.73   $63.75   $63.70  
  Purchase #2 $110.68   11.647%   $123.5709   $123.57   $123.55   $123.60  
  Purchase #3 $86.44   10.340%   $95.3779   $95.38   $95.40   $95.40  
  Purchase #4 $149.52   12.696%   $168.5031   $168.50   $168.50   $168.50  
  Purchase #5 $68.42   4.811%   $71.7117   $71.71   $71.70   $71.70  
  Purchase #6 $88.77   5.507%   $93.6586   $93.66   $93.65   $93.70  
  Purchase #7 $210.29   5.359%   $221.5594   $221.56   $221.55   $221.60  
  7 purchase totals = $774.48       $838.1109   $838.11   $838.10   $838.20