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	$166.88	11.613%	$186.2598	$186.26	$186.25	$186.30
Purchase #2	$88.30	10.506%	$97.5768	$97.58	$97.60	$97.60
Purchase #3	$210.26	8.423%	$227.9702	$227.97	$227.95	$228.00
Purchase #4	$18.32	12.612%	$20.6305	$20.63	$20.65	$20.60
Purchase #5	$5.59	5.736%	$5.9106	$5.91	$5.90	$5.90
Purchase #6	$78.66	13.736%	$89.4647	$89.46	$89.45	$89.50
Purchase #7	$163.88	3.173%	$169.0799	$169.08	$169.10	$169.10
7 purchase totals =	$731.89		$796.8925	$796.89	$796.90	$797.00