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	$12.25	5.850%	$12.9666	$12.97	$12.95	$13.00
Purchase #2	$193.45	8.724%	$210.3266	$210.33	$210.35	$210.30
Purchase #3	$82.86	10.211%	$91.3208	$91.32	$91.30	$91.30
Purchase #4	$88.39	4.234%	$92.1324	$92.13	$92.15	$92.10
Purchase #5	$162.89	3.313%	$168.2865	$168.29	$168.30	$168.30
Purchase #6	$112.76	11.104%	$125.2809	$125.28	$125.30	$125.30
Purchase #7	$60.87	9.320%	$66.5431	$66.54	$66.55	$66.50
7 purchase totals =	$713.47		$766.8569	$766.86	$766.90	$766.80