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	$104.98	6.192%	$111.4804	$111.48	$111.50	$111.50
Purchase #2	$44.62	9.865%	$49.0218	$49.02	$49.00	$49.00
Purchase #3	$64.77	10.433%	$71.5275	$71.53	$71.55	$71.50
Purchase #4	$159.73	12.410%	$179.5525	$179.55	$179.55	$179.60
Purchase #5	$83.90	6.272%	$89.1622	$89.16	$89.15	$89.20
Purchase #6	$227.72	3.212%	$235.0344	$235.03	$235.05	$235.00
Purchase #7	$223.73	5.358%	$235.7175	$235.72	$235.70	$235.70
7 purchase totals =	$909.45		$971.4963	$971.49	$971.50	$971.50