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	$90.78	9.623%	$99.5158	$99.52	$99.50	$99.50
Purchase #2	$105.32	10.674%	$116.5619	$116.56	$116.55	$116.60
Purchase #3	$46.31	10.807%	$51.3147	$51.31	$51.30	$51.30
Purchase #4	$165.75	12.548%	$186.5483	$186.55	$186.55	$186.50
Purchase #5	$100.89	8.764%	$109.732	$109.73	$109.75	$109.70
Purchase #6	$128.79	3.483%	$133.2758	$133.28	$133.30	$133.30
Purchase #7	$163.95	10.195%	$180.6647	$180.66	$180.65	$180.70
7 purchase totals =	$801.79		$877.6132	$877.61	$877.60	$877.60