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	$7.77	7.705%	$8.3687	$8.37	$8.35	$8.40
Purchase #2	$116.89	12.453%	$131.4463	$131.45	$131.45	$131.40
Purchase #3	$79.65	7.426%	$85.5648	$85.56	$85.55	$85.60
Purchase #4	$5.41	4.871%	$5.6735	$5.67	$5.65	$5.70
Purchase #5	$171.64	5.218%	$180.5962	$180.60	$180.60	$180.60
Purchase #6	$89.38	10.810%	$99.042	$99.04	$99.05	$99.00
Purchase #7	$173.52	11.148%	$192.864	$192.86	$192.85	$192.90
7 purchase totals =	$644.26		$703.5555	$703.55	$703.50	$703.60