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	$86.39	7.125%	$92.5453	$92.55	$92.55	$92.50
Purchase #2	$236.76	5.848%	$250.6057	$250.61	$250.60	$250.60
Purchase #3	$77.30	10.570%	$85.4706	$85.47	$85.45	$85.50
Purchase #4	$195.34	4.511%	$204.1518	$204.15	$204.15	$204.20
Purchase #5	$36.64	10.844%	$40.6132	$40.61	$40.60	$40.60
Purchase #6	$228.83	6.140%	$242.8802	$242.88	$242.90	$242.90
Purchase #7	$63.84	4.133%	$66.4785	$66.48	$66.50	$66.50
7 purchase totals =	$925.10		$982.7453	$982.75	$982.75	$982.80