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	$182.73	3.802%	$189.6774	$189.68	$189.70	$189.70
Purchase #2	$104.74	5.455%	$110.4536	$110.45	$110.45	$110.50
Purchase #3	$44.43	3.326%	$45.9077	$45.91	$45.90	$45.90
Purchase #4	$175.31	5.268%	$184.5453	$184.55	$184.55	$184.50
Purchase #5	$228.96	7.414%	$245.9351	$245.94	$245.95	$245.90
Purchase #6	$146.31	12.613%	$164.7641	$164.76	$164.75	$164.80
Purchase #7	$124.65	3.171%	$128.6027	$128.60	$128.60	$128.60
7 purchase totals =	$1,007.13		$1,069.8859	$1,069.89	$1,069.90	$1,069.90