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 $136.71   6.802%   $146.009   $146.01   $146.00   $146.00  
  Purchase #2 $162.89   7.391%   $174.9292   $174.93   $174.95   $174.90  
  Purchase #3 $51.42   13.732%   $58.481   $58.48   $58.50   $58.50  
  Purchase #4 $156.73   8.303%   $169.7433   $169.74   $169.75   $169.70  
  Purchase #5 $74.99   6.124%   $79.5824   $79.58   $79.60   $79.60  
  Purchase #6 $13.86   12.467%   $15.5879   $15.59   $15.60   $15.60  
  Purchase #7 $161.45   5.780%   $170.7818   $170.78   $170.80   $170.80  
  7 purchase totals = $758.05       $815.1146   $815.11   $815.20   $815.10