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	$36.37	12.120%	$40.778	$40.78	$40.80	$40.80
Purchase #2	$34.76	12.865%	$39.2319	$39.23	$39.25	$39.20
Purchase #3	$107.99	10.272%	$119.0827	$119.08	$119.10	$119.10
Purchase #4	$62.81	13.109%	$71.0438	$71.04	$71.05	$71.00
Purchase #5	$67.32	6.633%	$71.7853	$71.79	$71.80	$71.80
Purchase #6	$93.46	4.677%	$97.8311	$97.83	$97.85	$97.80
Purchase #7	$105.74	12.223%	$118.6646	$118.66	$118.65	$118.70
7 purchase totals =	$508.45		$558.4174	$558.41	$558.50	$558.40