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	$74.42	5.837%	$78.7639	$78.76	$78.75	$78.80
Purchase #2	$217.66	9.684%	$238.7382	$238.74	$238.75	$238.70
Purchase #3	$143.35	12.433%	$161.1727	$161.17	$161.15	$161.20
Purchase #4	$100.69	9.558%	$110.314	$110.31	$110.30	$110.30
Purchase #5	$209.98	6.198%	$222.9946	$222.99	$223.00	$223.00
Purchase #6	$116.76	5.621%	$123.3231	$123.32	$123.30	$123.30
Purchase #7	$58.80	5.188%	$61.8505	$61.85	$61.85	$61.90
7 purchase totals =	$921.66		$997.1570	$997.14	$997.10	$997.20