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 $227.69   9.315%   $248.8993   $248.90   $248.90   $248.90  
  Purchase #2 $164.80   8.799%   $179.3008   $179.30   $179.30   $179.30  
  Purchase #3 $143.55   5.729%   $151.774   $151.77   $151.75   $151.80  
  Purchase #4 $216.92   10.140%   $238.9157   $238.92   $238.90   $238.90  
  Purchase #5 $88.80   6.296%   $94.3908   $94.39   $94.40   $94.40  
  Purchase #6 $248.56   7.347%   $266.8217   $266.82   $266.80   $266.80  
  Purchase #7 $231.36   9.138%   $252.5017   $252.50   $252.50   $252.50  
  7 purchase totals = $1,321.68       $1,432.6040   $1,432.60   $1,432.55   $1,432.60