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 $209.71   8.485%   $227.5039   $227.50   $227.50   $227.50  
  Purchase #2 $186.70   9.231%   $203.9343   $203.93   $203.95   $203.90  
  Purchase #3 $26.87   6.633%   $28.6523   $28.65   $28.65   $28.70  
  Purchase #4 $177.29   3.685%   $183.8231   $183.82   $183.80   $183.80  
  Purchase #5 $250.48   4.790%   $262.478   $262.48   $262.50   $262.50  
  Purchase #6 $241.38   11.125%   $268.2335   $268.23   $268.25   $268.20  
  Purchase #7 $84.43   9.639%   $92.5682   $92.57   $92.55   $92.60  
  7 purchase totals = $1,176.86       $1,267.1933   $1,267.18   $1,267.20   $1,267.20