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	$48.31	9.859%	$53.0729	$53.07	$53.05	$53.10
Purchase #2	$117.41	5.423%	$123.7771	$123.78	$123.80	$123.80
Purchase #3	$249.62	10.684%	$276.2894	$276.29	$276.30	$276.30
Purchase #4	$173.96	11.840%	$194.5569	$194.56	$194.55	$194.60
Purchase #5	$52.26	5.676%	$55.2263	$55.23	$55.25	$55.20
Purchase #6	$156.62	10.131%	$172.4872	$172.49	$172.50	$172.50
Purchase #7	$38.76	8.130%	$41.9112	$41.91	$41.90	$41.90
7 purchase totals =	$836.94		$917.3210	$917.33	$917.35	$917.40