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	$18.86	7.464%	$20.2677	$20.27	$20.25	$20.30
Purchase #2	$20.72	13.630%	$23.5441	$23.54	$23.55	$23.50
Purchase #3	$9.26	13.452%	$10.5057	$10.51	$10.50	$10.50
Purchase #4	$83.91	7.611%	$90.2964	$90.30	$90.30	$90.30
Purchase #5	$129.59	7.512%	$139.3248	$139.32	$139.30	$139.30
Purchase #6	$232.27	6.121%	$246.4872	$246.49	$246.50	$246.50
Purchase #7	$129.32	3.230%	$133.497	$133.50	$133.50	$133.50
7 purchase totals =	$623.93		$663.9229	$663.93	$663.90	$663.90