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	$63.84	11.870%	$71.4178	$71.42	$71.40	$71.40
Purchase #2	$227.77	11.533%	$254.0387	$254.04	$254.05	$254.00
Purchase #3	$245.85	12.847%	$277.4343	$277.43	$277.45	$277.40
Purchase #4	$78.62	13.636%	$89.3406	$89.34	$89.35	$89.30
Purchase #5	$223.97	13.367%	$253.9081	$253.91	$253.90	$253.90
Purchase #6	$217.89	10.617%	$241.0234	$241.02	$241.00	$241.00
Purchase #7	$38.76	9.633%	$42.4938	$42.49	$42.50	$42.50
7 purchase totals =	$1,096.70		$1,229.6567	$1,229.65	$1,229.65	$1,229.50