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 $247.81   6.672%   $264.3439   $264.34   $264.35   $264.30  
  Purchase #2 $29.94   11.436%   $33.3639   $33.36   $33.35   $33.40  
  Purchase #3 $88.65   11.124%   $98.5114   $98.51   $98.50   $98.50  
  Purchase #4 $18.60   4.321%   $19.4037   $19.40   $19.40   $19.40  
  Purchase #5 $212.42   7.154%   $227.6165   $227.62   $227.60   $227.60  
  Purchase #6 $61.66   8.241%   $66.7414   $66.74   $66.75   $66.70  
  Purchase #7 $197.97   9.359%   $216.498   $216.50   $216.50   $216.50  
  7 purchase totals = $857.05       $926.4788   $926.47   $926.45   $926.40