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	$30.29	6.453%	$32.2446	$32.24	$32.25	$32.20
Purchase #2	$59.44	11.851%	$66.4842	$66.48	$66.50	$66.50
Purchase #3	$118.27	4.152%	$123.1806	$123.18	$123.20	$123.20
Purchase #4	$133.67	9.463%	$146.3192	$146.32	$146.30	$146.30
Purchase #5	$190.93	4.526%	$199.5715	$199.57	$199.55	$199.60
Purchase #6	$32.87	12.418%	$36.9518	$36.95	$36.95	$37.00
Purchase #7	$195.48	11.772%	$218.4919	$218.49	$218.50	$218.50
7 purchase totals =	$760.95		$823.2438	$823.23	$823.25	$823.30