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	$53.64	3.178%	$55.3447	$55.34	$55.35	$55.30
Purchase #2	$206.37	5.369%	$217.45	$217.45	$217.45	$217.50
Purchase #3	$86.39	4.383%	$90.1765	$90.18	$90.20	$90.20
Purchase #4	$130.53	10.571%	$144.3283	$144.33	$144.35	$144.30
Purchase #5	$9.57	13.132%	$10.8267	$10.83	$10.85	$10.80
Purchase #6	$141.41	4.690%	$148.0421	$148.04	$148.05	$148.00
Purchase #7	$173.61	10.448%	$191.7488	$191.75	$191.75	$191.70
7 purchase totals =	$801.52		$857.9171	$857.92	$858.00	$857.80