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 $61.70   7.851%   $66.5441   $66.54   $66.55   $66.50  
  Purchase #2 $93.67   9.837%   $102.8843   $102.88   $102.90   $102.90  
  Purchase #3 $48.49   5.288%   $51.0542   $51.05   $51.05   $51.10  
  Purchase #4 $139.98   11.478%   $156.0469   $156.05   $156.05   $156.00  
  Purchase #5 $215.94   6.618%   $230.2309   $230.23   $230.25   $230.20  
  Purchase #6 $242.38   6.791%   $258.84   $258.84   $258.85   $258.80  
  Purchase #7 $151.55   3.697%   $157.1528   $157.15   $157.15   $157.20  
  7 purchase totals = $953.71       $1,022.7532   $1,022.74   $1,022.80   $1,022.70