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 $241.47   10.154%   $265.9889   $265.99   $266.00   $266.00  
  Purchase #2 $140.93   9.275%   $154.0013   $154.00   $154.00   $154.00  
  Purchase #3 $228.33   10.247%   $251.727   $251.73   $251.75   $251.70  
  Purchase #4 $135.90   10.641%   $150.3611   $150.36   $150.35   $150.40  
  Purchase #5 $89.89   8.852%   $97.8471   $97.85   $97.85   $97.80  
  Purchase #6 $78.31   12.263%   $87.9132   $87.91   $87.90   $87.90  
  Purchase #7 $235.92   9.527%   $258.3961   $258.40   $258.40   $258.40  
  7 purchase totals = $1,150.75       $1,266.2347   $1,266.24   $1,266.25   $1,266.20