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 $198.80   13.130%   $224.9024   $224.90   $224.90   $224.90  
  Purchase #2 $249.41   7.842%   $268.9687   $268.97   $268.95   $269.00  
  Purchase #3 $81.36   6.573%   $86.7078   $86.71   $86.70   $86.70  
  Purchase #4 $103.90   4.814%   $108.9017   $108.90   $108.90   $108.90  
  Purchase #5 $208.77   7.371%   $224.1584   $224.16   $224.15   $224.20  
  Purchase #6 $83.44   6.164%   $88.5832   $88.58   $88.60   $88.60  
  Purchase #7 $104.96   11.496%   $117.0262   $117.03   $117.05   $117.00  
  7 purchase totals = $1,030.64       $1,119.2484   $1,119.25   $1,119.25   $1,119.30