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 $209.86   10.792%   $232.5081   $232.51   $232.50   $232.50  
  Purchase #2 $54.60   13.844%   $62.1588   $62.16   $62.15   $62.20  
  Purchase #3 $247.49   5.250%   $260.4832   $260.48   $260.50   $260.50  
  Purchase #4 $46.68   13.411%   $52.9403   $52.94   $52.95   $52.90  
  Purchase #5 $29.64   6.757%   $31.6428   $31.64   $31.65   $31.60  
  Purchase #6 $170.80   10.542%   $188.8057   $188.81   $188.80   $188.80  
  Purchase #7 $52.89   3.102%   $54.5306   $54.53   $54.55   $54.50  
  7 purchase totals = $811.96       $883.0695   $883.07   $883.10   $883.00