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 $246.98   4.201%   $257.3556   $257.36   $257.35   $257.40  
  Purchase #2 $143.73   6.223%   $152.6743   $152.67   $152.65   $152.70  
  Purchase #3 $235.95   4.276%   $246.0392   $246.04   $246.05   $246.00  
  Purchase #4 $195.86   13.167%   $221.6489   $221.65   $221.65   $221.60  
  Purchase #5 $82.45   8.359%   $89.342   $89.34   $89.35   $89.30  
  Purchase #6 $209.69   10.307%   $231.3027   $231.30   $231.30   $231.30  
  Purchase #7 $56.53   13.617%   $64.2277   $64.23   $64.25   $64.20  
  7 purchase totals = $1,171.19       $1,262.5904   $1,262.59   $1,262.60   $1,262.50