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	$30.30	3.328%	$31.3084	$31.31	$31.30	$31.30
Purchase #2	$160.96	9.530%	$176.2995	$176.30	$176.30	$176.30
Purchase #3	$188.50	5.168%	$198.2417	$198.24	$198.25	$198.20
Purchase #4	$148.88	7.777%	$160.4584	$160.46	$160.45	$160.50
Purchase #5	$243.71	12.824%	$274.9634	$274.96	$274.95	$275.00
Purchase #6	$85.78	4.621%	$89.7439	$89.74	$89.75	$89.70
Purchase #7	$202.88	7.116%	$217.3169	$217.32	$217.30	$217.30
7 purchase totals =	$1,061.01		$1,148.3322	$1,148.33	$1,148.30	$1,148.30