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 $208.57   7.177%   $223.5391   $223.54   $223.55   $223.50  
  Purchase #2 $190.66   6.140%   $202.3665   $202.37   $202.35   $202.40  
  Purchase #3 $208.91   10.466%   $230.7745   $230.77   $230.75   $230.80  
  Purchase #4 $52.71   5.451%   $55.5832   $55.58   $55.60   $55.60  
  Purchase #5 $73.30   12.412%   $82.398   $82.40   $82.40   $82.40  
  Purchase #6 $143.77   3.435%   $148.7085   $148.71   $148.70   $148.70  
  Purchase #7 $200.64   7.742%   $216.1735   $216.17   $216.15   $216.20  
  7 purchase totals = $1,078.56       $1,159.5433   $1,159.54   $1,159.50   $1,159.60