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 $59.97   8.375%   $64.9925   $64.99   $65.00   $65.00  
  Purchase #2 $239.78   9.762%   $263.1873   $263.19   $263.20   $263.20  
  Purchase #3 $65.45   6.472%   $69.6859   $69.69   $69.70   $69.70  
  Purchase #4 $219.27   4.846%   $229.8958   $229.90   $229.90   $229.90  
  Purchase #5 $87.76   3.178%   $90.549   $90.55   $90.55   $90.50  
  Purchase #6 $94.86   13.284%   $107.4612   $107.46   $107.45   $107.50  
  Purchase #7 $112.67   6.264%   $119.7276   $119.73   $119.75   $119.70  
  7 purchase totals = $879.76       $945.4993   $945.51   $945.55   $945.50