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 $58.86   9.686%   $64.5612   $64.56   $64.55   $64.60  
  Purchase #2 $42.46   3.532%   $43.9597   $43.96   $43.95   $44.00  
  Purchase #3 $50.39   13.343%   $57.1135   $57.11   $57.10   $57.10  
  Purchase #4 $8.79   9.312%   $9.6085   $9.61   $9.60   $9.60  
  Purchase #5 $65.72   13.804%   $74.792   $74.79   $74.80   $74.80  
  Purchase #6 $241.79   5.355%   $254.7379   $254.74   $254.75   $254.70  
  Purchase #7 $239.91   8.442%   $260.1632   $260.16   $260.15   $260.20  
  7 purchase totals = $707.92       $764.9360   $764.93   $764.90   $765.00