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	$112.65	13.803%	$128.1991	$128.20	$128.20	$128.20
Purchase #2	$223.99	8.606%	$243.2666	$243.27	$243.25	$243.30
Purchase #3	$165.33	4.808%	$173.2791	$173.28	$173.30	$173.30
Purchase #4	$136.52	4.246%	$142.3166	$142.32	$142.30	$142.30
Purchase #5	$76.54	8.369%	$82.9456	$82.95	$82.95	$82.90
Purchase #6	$31.38	9.411%	$34.3332	$34.33	$34.35	$34.30
Purchase #7	$225.90	5.528%	$238.3878	$238.39	$238.40	$238.40
7 purchase totals =	$972.31		$1,042.7280	$1,042.74	$1,042.75	$1,042.70