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 $58.35   9.633%   $63.9709   $63.97   $63.95   $64.00  
  Purchase #2 $97.62   7.377%   $104.8214   $104.82   $104.80   $104.80  
  Purchase #3 $9.94   11.725%   $11.1055   $11.11   $11.10   $11.10  
  Purchase #4 $166.43   8.412%   $180.4301   $180.43   $180.45   $180.40  
  Purchase #5 $49.33   11.566%   $55.0355   $55.04   $55.05   $55.00  
  Purchase #6 $92.50   13.734%   $105.204   $105.20   $105.20   $105.20  
  Purchase #7 $37.88   9.211%   $41.3691   $41.37   $41.35   $41.40  
  7 purchase totals = $512.05       $561.9365   $561.94   $561.90   $561.90