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	$19.86	8.414%	$21.531	$21.53	$21.55	$21.50
Purchase #2	$220.95	13.102%	$249.8989	$249.90	$249.90	$249.90
Purchase #3	$36.47	13.266%	$41.3081	$41.31	$41.30	$41.30
Purchase #4	$134.74	3.213%	$139.0692	$139.07	$139.05	$139.10
Purchase #5	$197.50	12.528%	$222.2428	$222.24	$222.25	$222.20
Purchase #6	$37.80	12.157%	$42.3953	$42.40	$42.40	$42.40
Purchase #7	$65.54	6.518%	$69.8119	$69.81	$69.80	$69.80
7 purchase totals =	$712.86		$786.2572	$786.26	$786.25	$786.20