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 $117.73   6.241%   $125.0775   $125.08   $125.10   $125.10  
  Purchase #2 $182.91   9.825%   $200.8809   $200.88   $200.90   $200.90  
  Purchase #3 $121.66   12.330%   $136.6607   $136.66   $136.65   $136.70  
  Purchase #4 $28.66   7.401%   $30.7811   $30.78   $30.80   $30.80  
  Purchase #5 $62.58   11.341%   $69.6772   $69.68   $69.70   $69.70  
  Purchase #6 $34.39   8.375%   $37.2702   $37.27   $37.25   $37.30  
  Purchase #7 $85.52   8.312%   $92.6284   $92.63   $92.65   $92.60  
  7 purchase totals = $633.45       $692.9760   $692.98   $693.05   $693.10