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 $67.65   13.287%   $76.6387   $76.64   $76.65   $76.60  
  Purchase #2 $106.36   9.674%   $116.6493   $116.65   $116.65   $116.60  
  Purchase #3 $138.84   12.247%   $155.8437   $155.84   $155.85   $155.80  
  Purchase #4 $126.78   9.429%   $138.7341   $138.73   $138.75   $138.70  
  Purchase #5 $13.70   6.361%   $14.5715   $14.57   $14.55   $14.60  
  Purchase #6 $249.46   12.540%   $280.7423   $280.74   $280.75   $280.70  
  Purchase #7 $243.54   8.848%   $265.0884   $265.09   $265.10   $265.10  
  7 purchase totals = $946.33       $1,048.2680   $1,048.26   $1,048.30   $1,048.10