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 $33.53   7.225%   $35.9525   $35.95   $35.95   $36.00  
  Purchase #2 $118.85   3.823%   $123.3936   $123.39   $123.40   $123.40  
  Purchase #3 $30.68   9.208%   $33.505   $33.51   $33.50   $33.50  
  Purchase #4 $176.49   6.669%   $188.2601   $188.26   $188.25   $188.30  
  Purchase #5 $58.54   3.282%   $60.4613   $60.46   $60.45   $60.50  
  Purchase #6 $167.74   10.157%   $184.7774   $184.78   $184.80   $184.80  
  Purchase #7 $98.65   3.270%   $101.8759   $101.88   $101.90   $101.90  
  7 purchase totals = $684.48       $728.2258   $728.23   $728.25   $728.40