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 $221.68   12.621%   $249.6582   $249.66   $249.65   $249.70  
  Purchase #2 $125.70   4.581%   $131.4583   $131.46   $131.45   $131.50  
  Purchase #3 $247.64   13.812%   $281.844   $281.84   $281.85   $281.80  
  Purchase #4 $227.84   12.722%   $256.8258   $256.83   $256.85   $256.80  
  Purchase #5 $216.80   10.246%   $239.0133   $239.01   $239.00   $239.00  
  Purchase #6 $183.94   5.414%   $193.8985   $193.90   $193.90   $193.90  
  Purchase #7 $61.82   11.512%   $68.9367   $68.94   $68.95   $68.90  
  7 purchase totals = $1,285.42       $1,421.6348   $1,421.64   $1,421.65   $1,421.60