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 $59.43   7.722%   $64.0192   $64.02   $64.00   $64.00  
  Purchase #2 $153.51   4.165%   $159.9037   $159.90   $159.90   $159.90  
  Purchase #3 $67.53   3.795%   $70.0928   $70.09   $70.10   $70.10  
  Purchase #4 $176.78   7.809%   $190.5848   $190.58   $190.60   $190.60  
  Purchase #5 $186.56   10.668%   $206.4622   $206.46   $206.45   $206.50  
  Purchase #6 $56.62   13.374%   $64.1924   $64.19   $64.20   $64.20  
  Purchase #7 $195.47   4.147%   $203.5761   $203.58   $203.60   $203.60  
  7 purchase totals = $895.90       $958.8312   $958.82   $958.85   $958.90