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	$226.93	13.807%	$258.2622	$258.26	$258.25	$258.30
Purchase #2	$209.51	5.547%	$221.1315	$221.13	$221.15	$221.10
Purchase #3	$104.86	4.214%	$109.2788	$109.28	$109.30	$109.30
Purchase #4	$34.33	4.496%	$35.8735	$35.87	$35.85	$35.90
Purchase #5	$190.27	12.266%	$213.6085	$213.61	$213.60	$213.60
Purchase #6	$187.77	12.473%	$211.1906	$211.19	$211.20	$211.20
Purchase #7	$152.85	13.512%	$173.5031	$173.50	$173.50	$173.50
7 purchase totals =	$1,106.52		$1,222.8482	$1,222.84	$1,222.85	$1,222.90