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	$191.62	6.768%	$204.5888	$204.59	$204.60	$204.60
Purchase #2	$94.54	7.826%	$101.9387	$101.94	$101.95	$101.90
Purchase #3	$57.50	4.269%	$59.9547	$59.95	$59.95	$60.00
Purchase #4	$48.55	9.797%	$53.3064	$53.31	$53.30	$53.30
Purchase #5	$31.38	10.140%	$34.5619	$34.56	$34.55	$34.60
Purchase #6	$95.72	3.696%	$99.2578	$99.26	$99.25	$99.30
Purchase #7	$83.86	6.596%	$89.3914	$89.39	$89.40	$89.40
7 purchase totals =	$603.17		$642.9997	$643.00	$643.00	$643.10