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 $82.76   11.869%   $92.5828   $92.58   $92.60   $92.60  
  Purchase #2 $208.36   12.840%   $235.1134   $235.11   $235.10   $235.10  
  Purchase #3 $112.69   11.126%   $125.2279   $125.23   $125.25   $125.20  
  Purchase #4 $10.63   8.321%   $11.5145   $11.51   $11.50   $11.50  
  Purchase #5 $122.36   8.682%   $132.9833   $132.98   $133.00   $133.00  
  Purchase #6 $163.45   13.180%   $184.9927   $184.99   $185.00   $185.00  
  Purchase #7 $62.72   12.786%   $70.7394   $70.74   $70.75   $70.70  
  7 purchase totals = $762.97       $853.1540   $853.14   $853.20   $853.10