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	$250.54	6.393%	$266.557	$266.56	$266.55	$266.60
Purchase #2	$124.82	3.145%	$128.7456	$128.75	$128.75	$128.70
Purchase #3	$84.32	5.259%	$88.7544	$88.75	$88.75	$88.80
Purchase #4	$94.45	5.227%	$99.3869	$99.39	$99.40	$99.40
Purchase #5	$125.56	13.680%	$142.7366	$142.74	$142.75	$142.70
Purchase #6	$166.87	11.756%	$186.4872	$186.49	$186.50	$186.50
Purchase #7	$173.48	8.531%	$188.2796	$188.28	$188.30	$188.30
7 purchase totals =	$1,020.04		$1,100.9473	$1,100.96	$1,101.00	$1,101.00