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 $53.94   6.171%   $57.2686   $57.27   $57.25   $57.30  
  Purchase #2 $85.96   10.811%   $95.2531   $95.25   $95.25   $95.30  
  Purchase #3 $126.63   12.645%   $142.6424   $142.64   $142.65   $142.60  
  Purchase #4 $86.81   7.777%   $93.5612   $93.56   $93.55   $93.60  
  Purchase #5 $64.43   8.568%   $69.9504   $69.95   $69.95   $70.00  
  Purchase #6 $153.26   12.287%   $172.0911   $172.09   $172.10   $172.10  
  Purchase #7 $122.97   13.303%   $139.3287   $139.33   $139.35   $139.30  
  7 purchase totals = $694.00       $770.0955   $770.09   $770.10   $770.20