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 $179.33   7.304%   $192.4283   $192.43   $192.45   $192.40  
  Purchase #2 $241.70   13.553%   $274.4576   $274.46   $274.45   $274.50  
  Purchase #3 $188.88   6.380%   $200.9305   $200.93   $200.95   $200.90  
  Purchase #4 $35.58   13.337%   $40.3253   $40.33   $40.35   $40.30  
  Purchase #5 $197.25   4.690%   $206.501   $206.50   $206.50   $206.50  
  Purchase #6 $234.40   11.689%   $261.799   $261.80   $261.80   $261.80  
  Purchase #7 $126.91   10.413%   $140.1251   $140.13   $140.15   $140.10  
  7 purchase totals = $1,204.05       $1,316.5668   $1,316.58   $1,316.65   $1,316.50