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 $168.99   8.422%   $183.2223   $183.22   $183.20   $183.20  
  Purchase #2 $125.25   11.541%   $139.7051   $139.71   $139.70   $139.70  
  Purchase #3 $140.94   8.326%   $152.6747   $152.67   $152.65   $152.70  
  Purchase #4 $219.40   11.738%   $245.1532   $245.15   $245.15   $245.20  
  Purchase #5 $101.94   12.810%   $114.9985   $115.00   $115.00   $115.00  
  Purchase #6 $177.29   6.353%   $188.5532   $188.55   $188.55   $188.60  
  Purchase #7 $49.73   6.497%   $52.961   $52.96   $52.95   $53.00  
  7 purchase totals = $983.54       $1,077.2680   $1,077.26   $1,077.20   $1,077.40