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 $84.79   11.247%   $94.3263   $94.33   $94.35   $94.30  
  Purchase #2 $199.78   4.210%   $208.1907   $208.19   $208.20   $208.20  
  Purchase #3 $67.85   10.860%   $75.2185   $75.22   $75.20   $75.20  
  Purchase #4 $37.57   13.261%   $42.5522   $42.55   $42.55   $42.60  
  Purchase #5 $174.88   9.724%   $191.8853   $191.89   $191.90   $191.90  
  Purchase #6 $72.83   4.180%   $75.8743   $75.87   $75.85   $75.90  
  Purchase #7 $93.90   11.750%   $104.9333   $104.93   $104.95   $104.90  
  7 purchase totals = $731.60       $792.9806   $792.98   $793.00   $793.00