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 $210.28   10.502%   $232.3636   $232.36   $232.35   $232.40  
  Purchase #2 $243.94   13.404%   $276.6377   $276.64   $276.65   $276.60  
  Purchase #3 $78.28   7.484%   $84.1385   $84.14   $84.15   $84.10  
  Purchase #4 $227.58   13.620%   $258.5764   $258.58   $258.60   $258.60  
  Purchase #5 $147.61   10.817%   $163.577   $163.58   $163.60   $163.60  
  Purchase #6 $69.42   9.571%   $76.0642   $76.06   $76.05   $76.10  
  Purchase #7 $112.57   3.830%   $116.8814   $116.88   $116.90   $116.90  
  7 purchase totals = $1,089.68       $1,208.2388   $1,208.24   $1,208.30   $1,208.30