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 $224.58   13.248%   $254.3324   $254.33   $254.35   $254.30  
  Purchase #2 $216.70   12.856%   $244.559   $244.56   $244.55   $244.60  
  Purchase #3 $151.48   10.506%   $167.3945   $167.39   $167.40   $167.40  
  Purchase #4 $104.48   3.148%   $107.769   $107.77   $107.75   $107.80  
  Purchase #5 $134.82   5.106%   $141.7039   $141.70   $141.70   $141.70  
  Purchase #6 $122.26   9.544%   $133.9285   $133.93   $133.95   $133.90  
  Purchase #7 $164.41   12.468%   $184.9086   $184.91   $184.90   $184.90  
  7 purchase totals = $1,118.73       $1,234.5959   $1,234.59   $1,234.60   $1,234.60