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 $207.29   13.331%   $234.9238   $234.92   $234.90   $234.90  
  Purchase #2 $190.65   5.612%   $201.3493   $201.35   $201.35   $201.30  
  Purchase #3 $13.74   5.859%   $14.545   $14.55   $14.55   $14.50  
  Purchase #4 $42.54   9.256%   $46.4775   $46.48   $46.50   $46.50  
  Purchase #5 $195.66   6.355%   $208.0942   $208.09   $208.10   $208.10  
  Purchase #6 $152.70   6.211%   $162.1842   $162.18   $162.20   $162.20  
  Purchase #7 $136.56   3.408%   $141.214   $141.21   $141.20   $141.20  
  7 purchase totals = $939.14       $1,008.7880   $1,008.78   $1,008.80   $1,008.70