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 $119.78   4.355%   $124.9964   $125.00   $125.00   $125.00  
  Purchase #2 $67.45   12.151%   $75.6458   $75.65   $75.65   $75.60  
  Purchase #3 $229.61   11.573%   $256.1828   $256.18   $256.20   $256.20  
  Purchase #4 $41.73   8.819%   $45.4102   $45.41   $45.40   $45.40  
  Purchase #5 $168.93   10.561%   $186.7707   $186.77   $186.75   $186.80  
  Purchase #6 $152.38   9.303%   $166.5559   $166.56   $166.55   $166.60  
  Purchase #7 $179.46   3.807%   $186.292   $186.29   $186.30   $186.30  
  7 purchase totals = $959.34       $1,041.8538   $1,041.86   $1,041.85   $1,041.90