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 $238.68   12.248%   $267.9135   $267.91   $267.90   $267.90  
  Purchase #2 $207.38   5.621%   $219.0368   $219.04   $219.05   $219.00  
  Purchase #3 $200.34   6.195%   $212.7511   $212.75   $212.75   $212.80  
  Purchase #4 $63.78   7.473%   $68.5463   $68.55   $68.55   $68.50  
  Purchase #5 $101.80   12.266%   $114.2868   $114.29   $114.30   $114.30  
  Purchase #6 $18.68   11.632%   $20.8529   $20.85   $20.85   $20.90  
  Purchase #7 $60.50   8.512%   $65.6498   $65.65   $65.65   $65.60  
  7 purchase totals = $891.16       $969.0372   $969.04   $969.05   $969.00