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 $61.67   9.681%   $67.6403   $67.64   $67.65   $67.60  
  Purchase #2 $76.34   3.211%   $78.7913   $78.79   $78.80   $78.80  
  Purchase #3 $157.72   11.176%   $175.3468   $175.35   $175.35   $175.30  
  Purchase #4 $228.82   8.627%   $248.5603   $248.56   $248.55   $248.60  
  Purchase #5 $66.80   6.412%   $71.0832   $71.08   $71.10   $71.10  
  Purchase #6 $73.99   9.312%   $80.8799   $80.88   $80.90   $80.90  
  Purchase #7 $23.39   13.478%   $26.5425   $26.54   $26.55   $26.50  
  7 purchase totals = $688.73       $748.8443   $748.84   $748.90   $748.80