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 $208.38   12.157%   $233.7128   $233.71   $233.70   $233.70  
  Purchase #2 $26.96   11.444%   $30.0453   $30.05   $30.05   $30.00  
  Purchase #3 $94.98   9.572%   $104.0715   $104.07   $104.05   $104.10  
  Purchase #4 $244.97   10.193%   $269.9398   $269.94   $269.95   $269.90  
  Purchase #5 $63.86   8.631%   $69.3718   $69.37   $69.35   $69.40  
  Purchase #6 $248.37   10.351%   $274.0788   $274.08   $274.10   $274.10  
  Purchase #7 $246.51   5.640%   $260.4132   $260.41   $260.40   $260.40  
  7 purchase totals = $1,134.03       $1,241.6332   $1,241.63   $1,241.60   $1,241.60