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	$22.76	9.402%	$24.8999	$24.90	$24.90	$24.90
Purchase #2	$139.60	8.452%	$151.399	$151.40	$151.40	$151.40
Purchase #3	$206.56	4.612%	$216.0865	$216.09	$216.10	$216.10
Purchase #4	$18.84	9.289%	$20.59	$20.59	$20.60	$20.60
Purchase #5	$153.69	4.640%	$160.8212	$160.82	$160.80	$160.80
Purchase #6	$85.47	4.521%	$89.3341	$89.33	$89.35	$89.30
Purchase #7	$230.98	3.160%	$238.279	$238.28	$238.30	$238.30
7 purchase totals =	$857.90		$901.4097	$901.41	$901.45	$901.40