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	$117.50	9.597%	$128.7765	$128.78	$128.80	$128.80
Purchase #2	$190.37	10.400%	$210.1685	$210.17	$210.15	$210.20
Purchase #3	$113.97	8.173%	$123.2848	$123.28	$123.30	$123.30
Purchase #4	$226.78	9.119%	$247.4601	$247.46	$247.45	$247.50
Purchase #5	$31.90	9.618%	$34.9681	$34.97	$34.95	$35.00
Purchase #6	$88.62	12.473%	$99.6736	$99.67	$99.65	$99.70
Purchase #7	$77.33	8.126%	$83.6138	$83.61	$83.60	$83.60
7 purchase totals =	$846.47		$927.9454	$927.94	$927.90	$928.10