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 $72.79   5.594%   $76.8619   $76.86   $76.85   $76.90  
  Purchase #2 $235.80   5.694%   $249.2265   $249.23   $249.25   $249.20  
  Purchase #3 $67.60   12.396%   $75.9797   $75.98   $76.00   $76.00  
  Purchase #4 $114.42   10.808%   $126.7865   $126.79   $126.80   $126.80  
  Purchase #5 $71.81   9.452%   $78.5975   $78.60   $78.60   $78.60  
  Purchase #6 $140.48   11.589%   $156.7602   $156.76   $156.75   $156.80  
  Purchase #7 $238.57   3.679%   $247.347   $247.35   $247.35   $247.30  
  7 purchase totals = $941.47       $1,011.5593   $1,011.57   $1,011.60   $1,011.60