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	$186.74	13.754%	$212.4242	$212.42	$212.40	$212.40
Purchase #2	$137.73	10.117%	$151.6641	$151.66	$151.65	$151.70
Purchase #3	$15.84	11.470%	$17.6568	$17.66	$17.65	$17.70
Purchase #4	$69.62	12.591%	$78.3859	$78.39	$78.40	$78.40
Purchase #5	$94.33	5.127%	$99.1663	$99.17	$99.15	$99.20
Purchase #6	$196.81	12.712%	$221.8285	$221.83	$221.85	$221.80
Purchase #7	$7.46	10.808%	$8.2663	$8.27	$8.25	$8.30
7 purchase totals =	$708.53		$789.3921	$789.40	$789.35	$789.50