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	$35.83	8.121%	$38.7398	$38.74	$38.75	$38.70
Purchase #2	$96.90	6.861%	$103.5483	$103.55	$103.55	$103.50
Purchase #3	$107.86	11.142%	$119.8778	$119.88	$119.90	$119.90
Purchase #4	$57.25	7.600%	$61.601	$61.60	$61.60	$61.60
Purchase #5	$221.81	9.403%	$242.6668	$242.67	$242.65	$242.70
Purchase #6	$91.72	5.501%	$96.7655	$96.77	$96.75	$96.80
Purchase #7	$68.50	12.790%	$77.2612	$77.26	$77.25	$77.30
7 purchase totals =	$679.87		$740.4604	$740.47	$740.45	$740.50