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	$156.77	5.818%	$165.8909	$165.89	$165.90	$165.90
Purchase #2	$102.49	9.577%	$112.3055	$112.31	$112.30	$112.30
Purchase #3	$225.58	6.580%	$240.4232	$240.42	$240.40	$240.40
Purchase #4	$67.54	10.514%	$74.6412	$74.64	$74.65	$74.60
Purchase #5	$30.49	3.183%	$31.4605	$31.46	$31.45	$31.50
Purchase #6	$90.81	10.614%	$100.4486	$100.45	$100.45	$100.40
Purchase #7	$28.44	7.463%	$30.5625	$30.56	$30.55	$30.60
7 purchase totals =	$702.12		$755.7324	$755.73	$755.70	$755.70