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 $243.81   12.497%   $274.2789   $274.28   $274.30   $274.30  
  Purchase #2 $84.94   3.818%   $88.183   $88.18   $88.20   $88.20  
  Purchase #3 $152.49   6.730%   $162.7526   $162.75   $162.75   $162.80  
  Purchase #4 $225.93   4.652%   $236.4403   $236.44   $236.45   $236.40  
  Purchase #5 $49.58   10.380%   $54.7264   $54.73   $54.75   $54.70  
  Purchase #6 $175.83   13.215%   $199.0659   $199.07   $199.05   $199.10  
  Purchase #7 $82.98   11.337%   $92.3874   $92.39   $92.40   $92.40  
  7 purchase totals = $1,015.56       $1,107.8345   $1,107.84   $1,107.90   $1,107.90