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	$239.27	10.620%	$264.6805	$264.68	$264.70	$264.70
Purchase #2	$125.44	13.262%	$142.0759	$142.08	$142.10	$142.10
Purchase #3	$243.43	8.159%	$263.2915	$263.29	$263.30	$263.30
Purchase #4	$152.76	10.452%	$168.7265	$168.73	$168.75	$168.70
Purchase #5	$70.97	9.288%	$77.5617	$77.56	$77.55	$77.60
Purchase #6	$42.57	6.428%	$45.3064	$45.31	$45.30	$45.30
Purchase #7	$34.50	13.550%	$39.1748	$39.17	$39.15	$39.20
7 purchase totals =	$908.94		$1,000.8173	$1,000.82	$1,000.85	$1,000.90