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	$74.82	8.468%	$81.1558	$81.16	$81.15	$81.20
Purchase #2	$73.41	12.629%	$82.6809	$82.68	$82.70	$82.70
Purchase #3	$229.88	3.553%	$238.0476	$238.05	$238.05	$238.00
Purchase #4	$96.88	7.475%	$104.1218	$104.12	$104.10	$104.10
Purchase #5	$116.79	3.384%	$120.7422	$120.74	$120.75	$120.70
Purchase #6	$211.82	5.148%	$222.7245	$222.72	$222.70	$222.70
Purchase #7	$42.64	7.435%	$45.8103	$45.81	$45.80	$45.80
7 purchase totals =	$846.24		$895.2831	$895.28	$895.25	$895.20