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 $68.63   7.794%   $73.979   $73.98   $74.00   $74.00  
  Purchase #2 $49.80   5.836%   $52.7063   $52.71   $52.70   $52.70  
  Purchase #3 $40.64   13.506%   $46.1288   $46.13   $46.15   $46.10  
  Purchase #4 $157.56   8.402%   $170.7982   $170.80   $170.80   $170.80  
  Purchase #5 $148.61   10.407%   $164.0758   $164.08   $164.10   $164.10  
  Purchase #6 $175.69   13.803%   $199.9405   $199.94   $199.95   $199.90  
  Purchase #7 $13.29   6.269%   $14.1232   $14.12   $14.10   $14.10  
  7 purchase totals = $654.22       $721.7518   $721.76   $721.80   $721.70