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 $82.69   11.273%   $92.0116   $92.01   $92.00   $92.00  
  Purchase #2 $19.59   10.655%   $21.6773   $21.68   $21.70   $21.70  
  Purchase #3 $149.95   9.642%   $164.4082   $164.41   $164.40   $164.40  
  Purchase #4 $209.29   6.355%   $222.5904   $222.59   $222.60   $222.60  
  Purchase #5 $20.92   3.180%   $21.5853   $21.59   $21.60   $21.60  
  Purchase #6 $202.35   13.460%   $229.5863   $229.59   $229.60   $229.60  
  Purchase #7 $16.83   6.779%   $17.9709   $17.97   $17.95   $18.00  
  7 purchase totals = $701.62       $769.8300   $769.84   $769.85   $769.90