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 $184.27   11.447%   $205.3634   $205.36   $205.35   $205.40  
  Purchase #2 $235.36   13.424%   $266.9547   $266.95   $266.95   $267.00  
  Purchase #3 $115.42   6.221%   $122.6003   $122.60   $122.60   $122.60  
  Purchase #4 $114.64   10.422%   $126.5878   $126.59   $126.60   $126.60  
  Purchase #5 $22.75   11.429%   $25.3501   $25.35   $25.35   $25.40  
  Purchase #6 $216.73   4.747%   $227.0182   $227.02   $227.00   $227.00  
  Purchase #7 $242.45   10.202%   $267.1847   $267.18   $267.20   $267.20  
  7 purchase totals = $1,131.62       $1,241.0592   $1,241.05   $1,241.05   $1,241.20