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	$109.80	9.317%	$120.0301	$120.03	$120.05	$120.00
Purchase #2	$6.26	12.150%	$7.0206	$7.02	$7.00	$7.00
Purchase #3	$64.30	12.138%	$72.1047	$72.10	$72.10	$72.10
Purchase #4	$45.56	6.174%	$48.3729	$48.37	$48.35	$48.40
Purchase #5	$136.61	10.631%	$151.133	$151.13	$151.15	$151.10
Purchase #6	$172.84	10.410%	$190.8326	$190.83	$190.85	$190.80
Purchase #7	$173.78	10.457%	$191.9522	$191.95	$191.95	$192.00
7 purchase totals =	$709.15		$781.4461	$781.43	$781.45	$781.40