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 $159.48   11.340%   $177.565   $177.57   $177.55   $177.60  
  Purchase #2 $181.83   5.733%   $192.2543   $192.25   $192.25   $192.30  
  Purchase #3 $17.74   8.593%   $19.2644   $19.26   $19.25   $19.30  
  Purchase #4 $16.58   10.606%   $18.3385   $18.34   $18.35   $18.30  
  Purchase #5 $232.64   12.160%   $260.929   $260.93   $260.95   $260.90  
  Purchase #6 $236.76   4.445%   $247.284   $247.28   $247.30   $247.30  
  Purchase #7 $135.30   3.628%   $140.2087   $140.21   $140.20   $140.20  
  7 purchase totals = $980.33       $1,055.8439   $1,055.84   $1,055.85   $1,055.90