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 $42.51   11.346%   $47.3332   $47.33   $47.35   $47.30  
  Purchase #2 $86.73   10.730%   $96.0361   $96.04   $96.05   $96.00  
  Purchase #3 $106.37   7.767%   $114.6318   $114.63   $114.65   $114.60  
  Purchase #4 $91.60   3.393%   $94.708   $94.71   $94.70   $94.70  
  Purchase #5 $189.99   10.221%   $209.4089   $209.41   $209.40   $209.40  
  Purchase #6 $65.63   12.138%   $73.5962   $73.60   $73.60   $73.60  
  Purchase #7 $117.95   6.446%   $125.5531   $125.55   $125.55   $125.60  
  7 purchase totals = $700.78       $761.2673   $761.27   $761.30   $761.20