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	$26.76	4.134%	$27.8663	$27.87	$27.85	$27.90
Purchase #2	$150.36	8.212%	$162.7076	$162.71	$162.70	$162.70
Purchase #3	$128.45	3.396%	$132.8122	$132.81	$132.80	$132.80
Purchase #4	$209.72	11.339%	$233.5002	$233.50	$233.50	$233.50
Purchase #5	$38.72	3.765%	$40.1778	$40.18	$40.20	$40.20
Purchase #6	$93.88	6.463%	$99.9475	$99.95	$99.95	$99.90
Purchase #7	$232.74	9.298%	$254.3802	$254.38	$254.40	$254.40
7 purchase totals =	$880.63		$951.3918	$951.40	$951.40	$951.40