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 $96.33   8.142%   $104.1732   $104.17   $104.15   $104.20  
  Purchase #2 $205.93   5.196%   $216.6301   $216.63   $216.65   $216.60  
  Purchase #3 $151.36   13.511%   $171.8102   $171.81   $171.80   $171.80  
  Purchase #4 $65.45   8.676%   $71.1284   $71.13   $71.15   $71.10  
  Purchase #5 $96.68   10.664%   $106.99   $106.99   $107.00   $107.00  
  Purchase #6 $25.93   12.581%   $29.1923   $29.19   $29.20   $29.20  
  Purchase #7 $222.46   4.714%   $232.9468   $232.95   $232.95   $232.90  
  7 purchase totals = $864.14       $932.8710   $932.87   $932.90   $932.80