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 $248.39   10.517%   $274.5132   $274.51   $274.50   $274.50  
  Purchase #2 $63.76   4.803%   $66.8224   $66.82   $66.80   $66.80  
  Purchase #3 $220.46   11.528%   $245.8746   $245.87   $245.85   $245.90  
  Purchase #4 $76.74   9.580%   $84.0917   $84.09   $84.10   $84.10  
  Purchase #5 $163.58   3.286%   $168.9552   $168.96   $168.95   $169.00  
  Purchase #6 $191.90   4.481%   $200.499   $200.50   $200.50   $200.50  
  Purchase #7 $145.61   13.152%   $164.7606   $164.76   $164.75   $164.80  
  7 purchase totals = $1,110.44       $1,205.5167   $1,205.51   $1,205.45   $1,205.60