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 $44.37   7.404%   $47.6552   $47.66   $47.65   $47.70  
  Purchase #2 $73.57   4.203%   $76.6621   $76.66   $76.65   $76.70  
  Purchase #3 $56.88   11.182%   $63.2403   $63.24   $63.25   $63.20  
  Purchase #4 $191.98   8.616%   $208.521   $208.52   $208.50   $208.50  
  Purchase #5 $18.29   13.250%   $20.7134   $20.71   $20.70   $20.70  
  Purchase #6 $195.96   13.812%   $223.026   $223.03   $223.05   $223.00  
  Purchase #7 $92.90   12.261%   $104.2905   $104.29   $104.30   $104.30  
  7 purchase totals = $673.95       $744.1085   $744.11   $744.10   $744.10