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	$173.59	5.185%	$182.5906	$182.59	$182.60	$182.60
Purchase #2	$142.49	8.304%	$154.3224	$154.32	$154.30	$154.30
Purchase #3	$91.59	9.160%	$99.9796	$99.98	$100.00	$100.00
Purchase #4	$249.61	10.487%	$275.7866	$275.79	$275.80	$275.80
Purchase #5	$196.34	12.398%	$220.6822	$220.68	$220.70	$220.70
Purchase #6	$60.32	5.276%	$63.5025	$63.50	$63.50	$63.50
Purchase #7	$38.93	8.851%	$42.3757	$42.38	$42.40	$42.40
7 purchase totals =	$952.87		$1,039.2396	$1,039.24	$1,039.30	$1,039.30