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	$65.53	8.181%	$70.891	$70.89	$70.90	$70.90
Purchase #2	$113.94	8.147%	$123.2227	$123.22	$123.20	$123.20
Purchase #3	$147.47	7.307%	$158.2456	$158.25	$158.25	$158.20
Purchase #4	$35.87	5.236%	$37.7482	$37.75	$37.75	$37.70
Purchase #5	$141.86	6.135%	$150.5631	$150.56	$150.55	$150.60
Purchase #6	$242.57	8.454%	$263.0769	$263.08	$263.10	$263.10
Purchase #7	$48.65	7.431%	$52.2652	$52.27	$52.25	$52.30
7 purchase totals =	$795.89		$856.0127	$856.02	$856.00	$856.00