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 $97.79   8.458%   $106.0611   $106.06   $106.05   $106.10  
  Purchase #2 $195.33   4.874%   $204.8504   $204.85   $204.85   $204.90  
  Purchase #3 $102.93   10.740%   $113.9847   $113.98   $114.00   $114.00  
  Purchase #4 $119.70   4.763%   $125.4013   $125.40   $125.40   $125.40  
  Purchase #5 $248.36   7.646%   $267.3496   $267.35   $267.35   $267.30  
  Purchase #6 $167.45   8.385%   $181.4907   $181.49   $181.50   $181.50  
  Purchase #7 $208.71   4.584%   $218.2773   $218.28   $218.30   $218.30  
  7 purchase totals = $1,140.27       $1,217.4151   $1,217.41   $1,217.45   $1,217.50