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	$156.78	9.389%	$171.5001	$171.50	$171.50	$171.50
Purchase #2	$49.56	11.114%	$55.0681	$55.07	$55.05	$55.10
Purchase #3	$59.59	10.607%	$65.9107	$65.91	$65.90	$65.90
Purchase #4	$133.71	8.783%	$145.4537	$145.45	$145.45	$145.50
Purchase #5	$20.48	3.278%	$21.1513	$21.15	$21.15	$21.20
Purchase #6	$231.38	10.427%	$255.506	$255.51	$255.50	$255.50
Purchase #7	$196.71	6.677%	$209.8443	$209.84	$209.85	$209.80
7 purchase totals =	$848.21		$924.4342	$924.43	$924.40	$924.50