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 $150.65   10.820%   $166.9503   $166.95   $166.95   $167.00  
  Purchase #2 $116.64   5.177%   $122.6785   $122.68   $122.70   $122.70  
  Purchase #3 $92.33   6.299%   $98.1459   $98.15   $98.15   $98.10  
  Purchase #4 $34.53   9.341%   $37.7554   $37.76   $37.75   $37.80  
  Purchase #5 $59.93   11.747%   $66.97   $66.97   $66.95   $67.00  
  Purchase #6 $16.69   8.620%   $18.1287   $18.13   $18.15   $18.10  
  Purchase #7 $63.97   4.509%   $66.8544   $66.85   $66.85   $66.90  
  7 purchase totals = $534.74       $577.4832   $577.49   $577.50   $577.60