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 $113.52   11.295%   $126.3421   $126.34   $126.35   $126.30  
  Purchase #2 $245.71   11.798%   $274.6989   $274.70   $274.70   $274.70  
  Purchase #3 $189.94   5.167%   $199.7542   $199.75   $199.75   $199.80  
  Purchase #4 $44.76   11.448%   $49.8841   $49.88   $49.90   $49.90  
  Purchase #5 $238.99   11.734%   $267.0331   $267.03   $267.05   $267.00  
  Purchase #6 $73.80   11.738%   $82.4626   $82.46   $82.45   $82.50  
  Purchase #7 $227.92   9.281%   $249.0733   $249.07   $249.05   $249.10  
  7 purchase totals = $1,134.64       $1,249.2483   $1,249.23   $1,249.25   $1,249.30