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 $213.56   6.402%   $227.2321   $227.23   $227.25   $227.20  
  Purchase #2 $250.57   11.299%   $278.8819   $278.88   $278.90   $278.90  
  Purchase #3 $22.30   6.481%   $23.7453   $23.75   $23.75   $23.70  
  Purchase #4 $226.74   9.725%   $248.7905   $248.79   $248.80   $248.80  
  Purchase #5 $27.25   3.415%   $28.1806   $28.18   $28.20   $28.20  
  Purchase #6 $133.39   11.454%   $148.6685   $148.67   $148.65   $148.70  
  Purchase #7 $106.66   11.733%   $119.1744   $119.17   $119.15   $119.20  
  7 purchase totals = $980.47       $1,074.6733   $1,074.67   $1,074.70   $1,074.70