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 $244.48   11.809%   $273.3506   $273.35   $273.35   $273.40  
  Purchase #2 $249.81   3.678%   $258.998   $259.00   $259.00   $259.00  
  Purchase #3 $83.86   4.773%   $87.8626   $87.86   $87.85   $87.90  
  Purchase #4 $206.49   13.205%   $233.757   $233.76   $233.75   $233.80  
  Purchase #5 $110.93   7.180%   $118.8948   $118.89   $118.90   $118.90  
  Purchase #6 $139.74   3.212%   $144.2284   $144.23   $144.25   $144.20  
  Purchase #7 $46.91   8.293%   $50.8002   $50.80   $50.80   $50.80  
  7 purchase totals = $1,082.22       $1,167.8916   $1,167.89   $1,167.90   $1,168.00