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 $204.99   10.727%   $226.9793   $226.98   $227.00   $227.00  
  Purchase #2 $72.30   5.752%   $76.4587   $76.46   $76.45   $76.50  
  Purchase #3 $87.30   6.841%   $93.2722   $93.27   $93.25   $93.30  
  Purchase #4 $175.56   5.272%   $184.8155   $184.82   $184.80   $184.80  
  Purchase #5 $189.38   4.440%   $197.7885   $197.79   $197.80   $197.80  
  Purchase #6 $202.83   6.431%   $215.874   $215.87   $215.85   $215.90  
  Purchase #7 $94.92   11.617%   $105.9469   $105.95   $105.95   $105.90  
  7 purchase totals = $1,027.28       $1,101.1351   $1,101.14   $1,101.10   $1,101.20