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 $190.98   8.175%   $206.5926   $206.59   $206.60   $206.60  
  Purchase #2 $236.64   13.596%   $268.8136   $268.81   $268.80   $268.80  
  Purchase #3 $52.64   11.253%   $58.5636   $58.56   $58.55   $58.60  
  Purchase #4 $64.51   4.340%   $67.3097   $67.31   $67.30   $67.30  
  Purchase #5 $198.79   10.730%   $220.1202   $220.12   $220.10   $220.10  
  Purchase #6 $164.57   4.434%   $171.867   $171.87   $171.85   $171.90  
  Purchase #7 $242.91   3.422%   $251.2224   $251.22   $251.20   $251.20  
  7 purchase totals = $1,151.04       $1,244.4891   $1,244.48   $1,244.40   $1,244.50