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 $52.44   4.423%   $54.7594   $54.76   $54.75   $54.80  
  Purchase #2 $249.93   9.302%   $273.1785   $273.18   $273.20   $273.20  
  Purchase #3 $119.75   8.804%   $130.2928   $130.29   $130.30   $130.30  
  Purchase #4 $39.65   6.276%   $42.1384   $42.14   $42.15   $42.10  
  Purchase #5 $213.97   11.826%   $239.2741   $239.27   $239.25   $239.30  
  Purchase #6 $177.32   4.152%   $184.6823   $184.68   $184.70   $184.70  
  Purchase #7 $224.52   5.175%   $236.1389   $236.14   $236.15   $236.10  
  7 purchase totals = $1,077.58       $1,160.4644   $1,160.46   $1,160.50   $1,160.50