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 $29.73   5.262%   $31.2944   $31.29   $31.30   $31.30  
  Purchase #2 $250.46   7.181%   $268.4455   $268.45   $268.45   $268.40  
  Purchase #3 $187.39   3.817%   $194.5427   $194.54   $194.55   $194.50  
  Purchase #4 $205.93   3.441%   $213.0161   $213.02   $213.00   $213.00  
  Purchase #5 $84.76   13.202%   $95.95   $95.95   $95.95   $96.00  
  Purchase #6 $241.38   4.543%   $252.3459   $252.35   $252.35   $252.30  
  Purchase #7 $177.43   12.732%   $200.0204   $200.02   $200.00   $200.00  
  7 purchase totals = $1,177.08       $1,255.6150   $1,255.62   $1,255.60   $1,255.50