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 $221.80   8.824%   $241.3716   $241.37   $241.35   $241.40  
  Purchase #2 $237.62   7.441%   $255.3013   $255.30   $255.30   $255.30  
  Purchase #3 $235.75   3.748%   $244.5859   $244.59   $244.60   $244.60  
  Purchase #4 $32.27   4.614%   $33.7589   $33.76   $33.75   $33.80  
  Purchase #5 $40.56   7.320%   $43.529   $43.53   $43.55   $43.50  
  Purchase #6 $219.48   13.324%   $248.7235   $248.72   $248.70   $248.70  
  Purchase #7 $244.45   8.411%   $265.0107   $265.01   $265.00   $265.00  
  7 purchase totals = $1,231.93       $1,332.2809   $1,332.28   $1,332.25   $1,332.30