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	$46.77	8.113%	$50.5645	$50.56	$50.55	$50.60
Purchase #2	$40.51	12.427%	$45.5442	$45.54	$45.55	$45.50
Purchase #3	$50.40	10.798%	$55.8422	$55.84	$55.85	$55.80
Purchase #4	$167.98	13.545%	$190.7329	$190.73	$190.75	$190.70
Purchase #5	$176.48	10.166%	$194.421	$194.42	$194.40	$194.40
Purchase #6	$176.81	6.619%	$188.5131	$188.51	$188.50	$188.50
Purchase #7	$197.26	12.790%	$222.4896	$222.49	$222.50	$222.50
7 purchase totals =	$856.21		$948.1075	$948.09	$948.10	$948.00