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 $233.31   11.148%   $259.3194   $259.32   $259.30   $259.30  
  Purchase #2 $145.81   5.730%   $154.1649   $154.16   $154.15   $154.20  
  Purchase #3 $31.26   11.204%   $34.7624   $34.76   $34.75   $34.80  
  Purchase #4 $44.99   8.786%   $48.9428   $48.94   $48.95   $48.90  
  Purchase #5 $170.35   9.361%   $186.2965   $186.30   $186.30   $186.30  
  Purchase #6 $218.38   12.360%   $245.3718   $245.37   $245.35   $245.40  
  Purchase #7 $247.48   13.300%   $280.3948   $280.39   $280.40   $280.40  
  7 purchase totals = $1,091.58       $1,209.2526   $1,209.24   $1,209.20   $1,209.30