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	$227.47	12.269%	$255.3783	$255.38	$255.40	$255.40
Purchase #2	$212.44	8.606%	$230.7226	$230.72	$230.70	$230.70
Purchase #3	$223.75	8.364%	$242.4645	$242.46	$242.45	$242.50
Purchase #4	$19.33	4.156%	$20.1334	$20.13	$20.15	$20.10
Purchase #5	$77.85	5.560%	$82.1785	$82.18	$82.20	$82.20
Purchase #6	$191.71	12.870%	$216.3831	$216.38	$216.40	$216.40
Purchase #7	$68.77	4.584%	$71.9224	$71.92	$71.90	$71.90
7 purchase totals =	$1,021.32		$1,119.1828	$1,119.17	$1,119.20	$1,119.20