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	$245.86	6.838%	$262.6719	$262.67	$262.65	$262.70
Purchase #2	$86.49	3.845%	$89.8155	$89.82	$89.80	$89.80
Purchase #3	$15.70	13.451%	$17.8118	$17.81	$17.80	$17.80
Purchase #4	$18.54	8.541%	$20.1235	$20.12	$20.10	$20.10
Purchase #5	$138.47	7.862%	$149.3565	$149.36	$149.35	$149.40
Purchase #6	$142.32	4.620%	$148.8952	$148.90	$148.90	$148.90
Purchase #7	$31.59	13.682%	$35.9121	$35.91	$35.90	$35.90
7 purchase totals =	$678.97		$724.5865	$724.59	$724.50	$724.60