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 $24.95   5.241%   $26.2576   $26.26   $26.25   $26.30  
  Purchase #2 $171.60   5.529%   $181.0878   $181.09   $181.10   $181.10  
  Purchase #3 $57.68   5.765%   $61.0053   $61.01   $61.00   $61.00  
  Purchase #4 $91.46   9.282%   $99.9493   $99.95   $99.95   $99.90  
  Purchase #5 $175.97   8.681%   $191.246   $191.25   $191.25   $191.20  
  Purchase #6 $27.56   10.355%   $30.4138   $30.41   $30.40   $30.40  
  Purchase #7 $245.55   9.283%   $268.3444   $268.34   $268.35   $268.30  
  7 purchase totals = $794.77       $858.3042   $858.31   $858.30   $858.20