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 $232.30   6.229%   $246.77   $246.77   $246.75   $246.80  
  Purchase #2 $134.83   11.404%   $150.206   $150.21   $150.20   $150.20  
  Purchase #3 $162.73   12.863%   $183.662   $183.66   $183.65   $183.70  
  Purchase #4 $87.90   5.716%   $92.9244   $92.92   $92.90   $92.90  
  Purchase #5 $26.73   6.781%   $28.5426   $28.54   $28.55   $28.50  
  Purchase #6 $65.87   13.524%   $74.7783   $74.78   $74.80   $74.80  
  Purchase #7 $222.33   4.420%   $232.157   $232.16   $232.15   $232.20  
  7 purchase totals = $932.69       $1,009.0403   $1,009.04   $1,009.00   $1,009.10