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 $247.52   13.549%   $281.0565   $281.06   $281.05   $281.10  
  Purchase #2 $232.66   5.601%   $245.6913   $245.69   $245.70   $245.70  
  Purchase #3 $200.69   13.448%   $227.6788   $227.68   $227.70   $227.70  
  Purchase #4 $133.40   11.192%   $148.3301   $148.33   $148.35   $148.30  
  Purchase #5 $18.37   10.518%   $20.3022   $20.30   $20.30   $20.30  
  Purchase #6 $122.29   3.260%   $126.2767   $126.28   $126.30   $126.30  
  Purchase #7 $16.71   9.377%   $18.2769   $18.28   $18.30   $18.30  
  7 purchase totals = $971.64       $1,067.6125   $1,067.62   $1,067.70   $1,067.70