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 $65.53   12.256%   $73.5614   $73.56   $73.55   $73.60  
  Purchase #2 $140.99   6.421%   $150.043   $150.04   $150.05   $150.00  
  Purchase #3 $135.27   6.518%   $144.0869   $144.09   $144.10   $144.10  
  Purchase #4 $163.99   5.191%   $172.5027   $172.50   $172.50   $172.50  
  Purchase #5 $192.94   12.285%   $216.6427   $216.64   $216.65   $216.60  
  Purchase #6 $91.87   7.645%   $98.8935   $98.89   $98.90   $98.90  
  Purchase #7 $114.80   13.175%   $129.9249   $129.92   $129.90   $129.90  
  7 purchase totals = $905.39       $985.6551   $985.64   $985.65   $985.60