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	$47.75	5.769%	$50.5047	$50.50	$50.50	$50.50
Purchase #2	$70.74	3.476%	$73.1989	$73.20	$73.20	$73.20
Purchase #3	$164.28	10.725%	$181.899	$181.90	$181.90	$181.90
Purchase #4	$51.91	7.196%	$55.6454	$55.65	$55.65	$55.60
Purchase #5	$131.46	11.328%	$146.3518	$146.35	$146.35	$146.40
Purchase #6	$209.43	8.661%	$227.5687	$227.57	$227.55	$227.60
Purchase #7	$45.96	4.654%	$48.099	$48.10	$48.10	$48.10
7 purchase totals =	$721.53		$783.2675	$783.27	$783.25	$783.30