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	$232.92	4.541%	$243.4969	$243.50	$243.50	$243.50
Purchase #2	$89.89	10.147%	$99.0111	$99.01	$99.00	$99.00
Purchase #3	$239.51	5.819%	$253.4471	$253.45	$253.45	$253.40
Purchase #4	$48.77	12.361%	$54.7985	$54.80	$54.80	$54.80
Purchase #5	$86.58	3.463%	$89.5783	$89.58	$89.60	$89.60
Purchase #6	$36.83	4.735%	$38.5739	$38.57	$38.55	$38.60
Purchase #7	$9.33	13.784%	$10.616	$10.62	$10.60	$10.60
7 purchase totals =	$743.83		$789.5218	$789.53	$789.50	$789.50