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	$185.80	6.654%	$198.1631	$198.16	$198.15	$198.20
Purchase #2	$59.62	7.166%	$63.8924	$63.89	$63.90	$63.90
Purchase #3	$59.28	12.640%	$66.773	$66.77	$66.75	$66.80
Purchase #4	$190.69	3.388%	$197.1506	$197.15	$197.15	$197.20
Purchase #5	$73.95	11.296%	$82.3034	$82.30	$82.30	$82.30
Purchase #6	$83.26	8.720%	$90.5203	$90.52	$90.50	$90.50
Purchase #7	$99.28	5.818%	$105.0561	$105.06	$105.05	$105.10
7 purchase totals =	$751.88		$803.8589	$803.85	$803.80	$804.00