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	$170.51	12.433%	$191.7095	$191.71	$191.70	$191.70
Purchase #2	$233.99	9.553%	$256.3431	$256.34	$256.35	$256.30
Purchase #3	$99.74	5.362%	$105.0881	$105.09	$105.10	$105.10
Purchase #4	$243.63	12.522%	$274.1373	$274.14	$274.15	$274.10
Purchase #5	$242.94	8.661%	$263.981	$263.98	$264.00	$264.00
Purchase #6	$130.52	7.145%	$139.8457	$139.85	$139.85	$139.80
Purchase #7	$88.49	3.707%	$91.7703	$91.77	$91.75	$91.80
7 purchase totals =	$1,209.82		$1,322.8750	$1,322.88	$1,322.90	$1,322.80