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	$111.52	3.759%	$115.712	$115.71	$115.70	$115.70
Purchase #2	$245.49	13.813%	$279.3995	$279.40	$279.40	$279.40
Purchase #3	$146.63	3.570%	$151.8647	$151.86	$151.85	$151.90
Purchase #4	$100.93	8.218%	$109.2244	$109.22	$109.20	$109.20
Purchase #5	$125.38	4.406%	$130.9042	$130.90	$130.90	$130.90
Purchase #6	$6.38	4.190%	$6.6473	$6.65	$6.65	$6.60
Purchase #7	$17.98	13.379%	$20.3855	$20.39	$20.40	$20.40
7 purchase totals =	$754.31		$814.1376	$814.13	$814.10	$814.10