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 $184.61   5.780%   $195.2805   $195.28   $195.30   $195.30  
  Purchase #2 $73.63   7.804%   $79.3761   $79.38   $79.40   $79.40  
  Purchase #3 $228.30   8.819%   $248.4338   $248.43   $248.45   $248.40  
  Purchase #4 $218.93   7.158%   $234.601   $234.60   $234.60   $234.60  
  Purchase #5 $244.33   6.528%   $260.2799   $260.28   $260.30   $260.30  
  Purchase #6 $83.57   11.640%   $93.2975   $93.30   $93.30   $93.30  
  Purchase #7 $173.57   13.362%   $196.7624   $196.76   $196.75   $196.80  
  7 purchase totals = $1,206.94       $1,308.0312   $1,308.03   $1,308.10   $1,308.10