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	$173.73	3.816%	$180.3595	$180.36	$180.35	$180.40
Purchase #2	$203.42	3.255%	$210.0413	$210.04	$210.05	$210.00
Purchase #3	$219.88	5.299%	$231.5314	$231.53	$231.55	$231.50
Purchase #4	$89.92	12.170%	$100.8633	$100.86	$100.85	$100.90
Purchase #5	$92.98	5.697%	$98.2771	$98.28	$98.30	$98.30
Purchase #6	$214.31	6.233%	$227.6679	$227.67	$227.65	$227.70
Purchase #7	$32.54	9.597%	$35.6629	$35.66	$35.65	$35.70
7 purchase totals =	$1,026.78		$1,084.4034	$1,084.40	$1,084.40	$1,084.50