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 $146.82   11.211%   $163.28   $163.28   $163.30   $163.30  
  Purchase #2 $58.61   12.265%   $65.7985   $65.80   $65.80   $65.80  
  Purchase #3 $228.87   9.505%   $250.6241   $250.62   $250.60   $250.60  
  Purchase #4 $104.56   9.152%   $114.1293   $114.13   $114.15   $114.10  
  Purchase #5 $181.83   8.846%   $197.9147   $197.91   $197.90   $197.90  
  Purchase #6 $238.67   7.260%   $255.9974   $256.00   $256.00   $256.00  
  Purchase #7 $242.63   6.425%   $258.219   $258.22   $258.20   $258.20  
  7 purchase totals = $1,201.99       $1,305.9630   $1,305.96   $1,305.95   $1,305.90