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 $244.62   11.360%   $272.4088   $272.41   $272.40   $272.40  
  Purchase #2 $224.89   4.436%   $234.8661   $234.87   $234.85   $234.90  
  Purchase #3 $99.31   8.503%   $107.7543   $107.75   $107.75   $107.80  
  Purchase #4 $125.98   6.566%   $134.2518   $134.25   $134.25   $134.30  
  Purchase #5 $192.93   5.383%   $203.3154   $203.32   $203.30   $203.30  
  Purchase #6 $83.56   11.250%   $92.9605   $92.96   $92.95   $93.00  
  Purchase #7 $20.67   4.802%   $21.6626   $21.66   $21.65   $21.70  
  7 purchase totals = $991.96       $1,067.2195   $1,067.22   $1,067.15   $1,067.40