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 $14.92   3.759%   $15.4808   $15.48   $15.50   $15.50  
  Purchase #2 $24.93   8.223%   $26.98   $26.98   $27.00   $27.00  
  Purchase #3 $171.74   8.855%   $186.9476   $186.95   $186.95   $186.90  
  Purchase #4 $194.77   7.553%   $209.481   $209.48   $209.50   $209.50  
  Purchase #5 $26.90   5.206%   $28.3004   $28.30   $28.30   $28.30  
  Purchase #6 $6.93   8.224%   $7.4999   $7.50   $7.50   $7.50  
  Purchase #7 $219.82   3.209%   $226.874   $226.87   $226.85   $226.90  
  7 purchase totals = $660.01       $701.5637   $701.56   $701.60   $701.60