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 $116.44   7.809%   $125.5328   $125.53   $125.55   $125.50  
  Purchase #2 $62.66   3.624%   $64.9308   $64.93   $64.95   $64.90  
  Purchase #3 $171.77   5.782%   $181.7017   $181.70   $181.70   $181.70  
  Purchase #4 $40.57   13.544%   $46.0648   $46.06   $46.05   $46.10  
  Purchase #5 $11.74   13.160%   $13.285   $13.29   $13.30   $13.30  
  Purchase #6 $205.43   12.409%   $230.9218   $230.92   $230.90   $230.90  
  Purchase #7 $32.40   11.166%   $36.0178   $36.02   $36.00   $36.00  
  7 purchase totals = $641.01       $698.4547   $698.45   $698.45   $698.40