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 $247.67   10.121%   $272.7367   $272.74   $272.75   $272.70  
  Purchase #2 $51.56   3.847%   $53.5435   $53.54   $53.55   $53.50  
  Purchase #3 $139.71   9.190%   $152.5493   $152.55   $152.55   $152.50  
  Purchase #4 $154.79   5.473%   $163.2617   $163.26   $163.25   $163.30  
  Purchase #5 $152.80   13.676%   $173.6969   $173.70   $173.70   $173.70  
  Purchase #6 $125.64   11.374%   $139.9303   $139.93   $139.95   $139.90  
  Purchase #7 $49.79   8.446%   $53.9953   $54.00   $54.00   $54.00  
  7 purchase totals = $921.96       $1,009.7137   $1,009.72   $1,009.75   $1,009.60