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	$93.56	12.415%	$105.1755	$105.18	$105.20	$105.20
Purchase #2	$101.91	8.772%	$110.8495	$110.85	$110.85	$110.80
Purchase #3	$155.75	10.334%	$171.8452	$171.85	$171.85	$171.80
Purchase #4	$201.83	11.865%	$225.7771	$225.78	$225.80	$225.80
Purchase #5	$221.65	5.123%	$233.0051	$233.01	$233.00	$233.00
Purchase #6	$48.34	13.135%	$54.6895	$54.69	$54.70	$54.70
Purchase #7	$34.99	11.742%	$39.0985	$39.10	$39.10	$39.10
7 purchase totals =	$858.03		$940.4404	$940.46	$940.50	$940.40