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	$89.75	4.646%	$93.9198	$93.92	$93.90	$93.90
Purchase #2	$149.80	10.759%	$165.917	$165.92	$165.90	$165.90
Purchase #3	$226.41	4.209%	$235.9396	$235.94	$235.95	$235.90
Purchase #4	$143.59	5.411%	$151.3597	$151.36	$151.35	$151.40
Purchase #5	$105.66	11.487%	$117.7972	$117.80	$117.80	$117.80
Purchase #6	$120.25	9.698%	$131.9118	$131.91	$131.90	$131.90
Purchase #7	$166.87	12.694%	$188.0525	$188.05	$188.05	$188.10
7 purchase totals =	$1,002.33		$1,084.8976	$1,084.90	$1,084.85	$1,084.90