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	$30.37	3.665%	$31.4831	$31.48	$31.50	$31.50
Purchase #2	$145.44	13.804%	$165.5165	$165.52	$165.50	$165.50
Purchase #3	$145.26	10.514%	$160.5326	$160.53	$160.55	$160.50
Purchase #4	$172.40	8.478%	$187.0161	$187.02	$187.00	$187.00
Purchase #5	$131.98	10.412%	$145.7218	$145.72	$145.70	$145.70
Purchase #6	$226.82	4.229%	$236.4122	$236.41	$236.40	$236.40
Purchase #7	$149.76	12.723%	$168.814	$168.81	$168.80	$168.80
7 purchase totals =	$1,002.03		$1,095.4963	$1,095.49	$1,095.45	$1,095.40