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	$17.42	4.550%	$18.2126	$18.21	$18.20	$18.20
Purchase #2	$39.61	12.517%	$44.568	$44.57	$44.55	$44.60
Purchase #3	$94.92	9.434%	$103.8748	$103.87	$103.85	$103.90
Purchase #4	$126.29	11.749%	$141.1278	$141.13	$141.15	$141.10
Purchase #5	$165.25	9.251%	$180.5373	$180.54	$180.55	$180.50
Purchase #6	$61.78	5.156%	$64.9654	$64.97	$64.95	$65.00
Purchase #7	$184.56	8.867%	$200.9249	$200.92	$200.90	$200.90
7 purchase totals =	$689.83		$754.2108	$754.21	$754.15	$754.20