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 $116.96   9.128%   $127.6361   $127.64   $127.65   $127.60  
  Purchase #2 $117.32   13.803%   $133.5137   $133.51   $133.50   $133.50  
  Purchase #3 $125.29   6.136%   $132.9778   $132.98   $133.00   $133.00  
  Purchase #4 $22.97   6.335%   $24.4251   $24.43   $24.45   $24.40  
  Purchase #5 $225.95   13.426%   $256.286   $256.29   $256.30   $256.30  
  Purchase #6 $133.65   3.422%   $138.2235   $138.22   $138.20   $138.20  
  Purchase #7 $52.95   3.807%   $54.9658   $54.97   $54.95   $55.00  
  7 purchase totals = $795.09       $868.0280   $868.04   $868.05   $868.00