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 $230.68   10.694%   $255.3489   $255.35   $255.35   $255.30  
  Purchase #2 $190.76   8.380%   $206.7457   $206.75   $206.75   $206.70  
  Purchase #3 $31.94   7.667%   $34.3888   $34.39   $34.40   $34.40  
  Purchase #4 $14.93   11.188%   $16.6004   $16.60   $16.60   $16.60  
  Purchase #5 $159.81   10.261%   $176.2081   $176.21   $176.20   $176.20  
  Purchase #6 $207.40   13.620%   $235.6479   $235.65   $235.65   $235.60  
  Purchase #7 $100.64   4.647%   $105.3167   $105.32   $105.30   $105.30  
  7 purchase totals = $936.16       $1,030.2565   $1,030.27   $1,030.25   $1,030.10