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	$113.66	8.601%	$123.4359	$123.44	$123.45	$123.40
Purchase #2	$32.53	8.121%	$35.1718	$35.17	$35.15	$35.20
Purchase #3	$217.58	12.425%	$244.6143	$244.61	$244.60	$244.60
Purchase #4	$136.88	3.637%	$141.8583	$141.86	$141.85	$141.90
Purchase #5	$90.74	3.730%	$94.1246	$94.12	$94.10	$94.10
Purchase #6	$230.38	10.358%	$254.2428	$254.24	$254.25	$254.20
Purchase #7	$85.32	4.814%	$89.4273	$89.43	$89.45	$89.40
7 purchase totals =	$907.09		$982.8750	$982.87	$982.85	$982.80