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	$248.65	6.231%	$264.1434	$264.14	$264.15	$264.10
Purchase #2	$81.76	10.790%	$90.5819	$90.58	$90.60	$90.60
Purchase #3	$96.70	13.568%	$109.8203	$109.82	$109.80	$109.80
Purchase #4	$135.66	9.849%	$149.0212	$149.02	$149.00	$149.00
Purchase #5	$165.29	6.669%	$176.3132	$176.31	$176.30	$176.30
Purchase #6	$110.73	5.191%	$116.478	$116.48	$116.50	$116.50
Purchase #7	$70.31	10.841%	$77.9323	$77.93	$77.95	$77.90
7 purchase totals =	$909.10		$984.2903	$984.28	$984.30	$984.20