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	$198.57	12.736%	$223.8599	$223.86	$223.85	$223.90
Purchase #2	$82.87	8.182%	$89.6504	$89.65	$89.65	$89.70
Purchase #3	$75.67	10.145%	$83.3467	$83.35	$83.35	$83.30
Purchase #4	$39.36	9.765%	$43.2035	$43.20	$43.20	$43.20
Purchase #5	$128.64	13.594%	$146.1273	$146.13	$146.15	$146.10
Purchase #6	$45.36	13.571%	$51.5158	$51.52	$51.50	$51.50
Purchase #7	$158.82	5.283%	$167.2105	$167.21	$167.20	$167.20
7 purchase totals =	$729.29		$804.9141	$804.92	$804.90	$804.90