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 $63.34   6.569%   $67.5008   $67.50   $67.50   $67.50  
  Purchase #2 $248.74   7.468%   $267.3159   $267.32   $267.30   $267.30  
  Purchase #3 $142.48   3.447%   $147.3913   $147.39   $147.40   $147.40  
  Purchase #4 $12.47   12.827%   $14.0695   $14.07   $14.05   $14.10  
  Purchase #5 $59.95   10.618%   $66.3155   $66.32   $66.30   $66.30  
  Purchase #6 $156.26   10.662%   $172.9204   $172.92   $172.90   $172.90  
  Purchase #7 $56.75   6.815%   $60.6175   $60.62   $60.60   $60.60  
  7 purchase totals = $739.99       $796.1309   $796.14   $796.05   $796.10