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	$54.27	3.214%	$56.0142	$56.01	$56.00	$56.00
Purchase #2	$113.97	4.320%	$118.8935	$118.89	$118.90	$118.90
Purchase #3	$76.55	7.298%	$82.1366	$82.14	$82.15	$82.10
Purchase #4	$11.56	13.433%	$13.1129	$13.11	$13.10	$13.10
Purchase #5	$77.56	5.869%	$82.112	$82.11	$82.10	$82.10
Purchase #6	$197.29	7.316%	$211.7237	$211.72	$211.70	$211.70
Purchase #7	$30.77	10.598%	$34.031	$34.03	$34.05	$34.00
7 purchase totals =	$561.97		$598.0239	$598.01	$598.00	$597.90