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 $207.69   13.601%   $235.9379   $235.94   $235.95   $235.90  
  Purchase #2 $164.25   7.691%   $176.8825   $176.88   $176.90   $176.90  
  Purchase #3 $13.99   9.793%   $15.36   $15.36   $15.35   $15.40  
  Purchase #4 $76.63   4.109%   $79.7787   $79.78   $79.80   $79.80  
  Purchase #5 $233.70   11.273%   $260.045   $260.05   $260.05   $260.00  
  Purchase #6 $134.80   11.246%   $149.9596   $149.96   $149.95   $150.00  
  Purchase #7 $221.92   3.136%   $228.8794   $228.88   $228.90   $228.90  
  7 purchase totals = $1,052.98       $1,146.8431   $1,146.85   $1,146.90   $1,146.90