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 $130.81   6.747%   $139.6358   $139.64   $139.65   $139.60  
  Purchase #2 $29.48   11.504%   $32.8714   $32.87   $32.85   $32.90  
  Purchase #3 $214.60   10.165%   $236.4141   $236.41   $236.40   $236.40  
  Purchase #4 $228.29   6.501%   $243.1311   $243.13   $243.15   $243.10  
  Purchase #5 $152.69   11.353%   $170.0249   $170.02   $170.00   $170.00  
  Purchase #6 $105.34   9.400%   $115.242   $115.24   $115.25   $115.20  
  Purchase #7 $170.95   7.378%   $183.5627   $183.56   $183.55   $183.60  
  7 purchase totals = $1,032.16       $1,120.8820   $1,120.87   $1,120.85   $1,120.80