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	$40.92	3.452%	$42.3326	$42.33	$42.35	$42.30
Purchase #2	$200.76	13.829%	$228.5231	$228.52	$228.50	$228.50
Purchase #3	$82.53	5.845%	$87.3539	$87.35	$87.35	$87.40
Purchase #4	$136.37	5.772%	$144.2413	$144.24	$144.25	$144.20
Purchase #5	$27.33	9.809%	$30.0108	$30.01	$30.00	$30.00
Purchase #6	$72.39	13.399%	$82.0895	$82.09	$82.10	$82.10
Purchase #7	$32.89	12.237%	$36.9147	$36.91	$36.90	$36.90
7 purchase totals =	$593.19		$651.4659	$651.45	$651.45	$651.40