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	$92.46	13.588%	$105.0235	$105.02	$105.00	$105.00
Purchase #2	$58.44	13.751%	$66.4761	$66.48	$66.50	$66.50
Purchase #3	$210.90	3.578%	$218.446	$218.45	$218.45	$218.40
Purchase #4	$174.60	11.515%	$194.7052	$194.71	$194.70	$194.70
Purchase #5	$72.83	6.724%	$77.7271	$77.73	$77.75	$77.70
Purchase #6	$87.40	6.147%	$92.7725	$92.77	$92.75	$92.80
Purchase #7	$72.72	4.142%	$75.7321	$75.73	$75.75	$75.70
7 purchase totals =	$769.35		$830.8825	$830.89	$830.90	$830.80