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 $71.57   5.404%   $75.4376   $75.44   $75.45   $75.40  
  Purchase #2 $92.60   9.496%   $101.3933   $101.39   $101.40   $101.40  
  Purchase #3 $185.71   12.189%   $208.3462   $208.35   $208.35   $208.30  
  Purchase #4 $76.61   9.592%   $83.9584   $83.96   $83.95   $84.00  
  Purchase #5 $104.50   8.689%   $113.58   $113.58   $113.60   $113.60  
  Purchase #6 $55.44   8.263%   $60.021   $60.02   $60.00   $60.00  
  Purchase #7 $220.41   9.586%   $241.5385   $241.54   $241.55   $241.50  
  7 purchase totals = $806.84       $884.2750   $884.28   $884.30   $884.20