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 $92.85   5.817%   $98.2511   $98.25   $98.25   $98.30  
  Purchase #2 $210.73   13.660%   $239.5157   $239.52   $239.50   $239.50  
  Purchase #3 $75.66   5.493%   $79.816   $79.82   $79.80   $79.80  
  Purchase #4 $194.38   6.232%   $206.4938   $206.49   $206.50   $206.50  
  Purchase #5 $149.34   11.779%   $166.9308   $166.93   $166.95   $166.90  
  Purchase #6 $113.28   4.160%   $117.9924   $117.99   $118.00   $118.00  
  Purchase #7 $238.99   3.551%   $247.4765   $247.48   $247.50   $247.50  
  7 purchase totals = $1,075.23       $1,156.4763   $1,156.48   $1,156.50   $1,156.50