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 $244.25   12.571%   $274.9547   $274.95   $274.95   $275.00  
  Purchase #2 $207.74   6.417%   $221.0707   $221.07   $221.05   $221.10  
  Purchase #3 $171.67   4.657%   $179.6647   $179.66   $179.65   $179.70  
  Purchase #4 $49.55   7.341%   $53.1875   $53.19   $53.20   $53.20  
  Purchase #5 $125.78   6.470%   $133.918   $133.92   $133.90   $133.90  
  Purchase #6 $89.56   3.622%   $92.8039   $92.80   $92.80   $92.80  
  Purchase #7 $110.82   11.860%   $123.9633   $123.96   $123.95   $124.00  
  7 purchase totals = $999.37       $1,079.5628   $1,079.55   $1,079.50   $1,079.70