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 $197.45   6.261%   $209.8123   $209.81   $209.80   $209.80  
  Purchase #2 $249.94   9.385%   $273.3969   $273.40   $273.40   $273.40  
  Purchase #3 $127.90   12.191%   $143.4923   $143.49   $143.50   $143.50  
  Purchase #4 $169.45   5.169%   $178.2089   $178.21   $178.20   $178.20  
  Purchase #5 $55.96   7.552%   $60.1861   $60.19   $60.20   $60.20  
  Purchase #6 $207.61   9.308%   $226.9343   $226.93   $226.95   $226.90  
  Purchase #7 $229.63   8.129%   $248.2966   $248.30   $248.30   $248.30  
  7 purchase totals = $1,237.94       $1,340.3274   $1,340.33   $1,340.35   $1,340.30