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	$66.98	7.760%	$72.1776	$72.18	$72.20	$72.20
Purchase #2	$200.41	13.434%	$227.3331	$227.33	$227.35	$227.30
Purchase #3	$250.36	3.263%	$258.5292	$258.53	$258.55	$258.50
Purchase #4	$162.39	6.808%	$173.4455	$173.45	$173.45	$173.40
Purchase #5	$211.90	4.439%	$221.3062	$221.31	$221.30	$221.30
Purchase #6	$21.91	10.565%	$24.2248	$24.22	$24.20	$24.20
Purchase #7	$67.27	9.218%	$73.4709	$73.47	$73.45	$73.50
7 purchase totals =	$981.22		$1,050.4873	$1,050.49	$1,050.50	$1,050.40