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	$109.58	10.141%	$120.6925	$120.69	$120.70	$120.70
Purchase #2	$73.79	13.469%	$83.7288	$83.73	$83.75	$83.70
Purchase #3	$78.97	4.476%	$82.5047	$82.50	$82.50	$82.50
Purchase #4	$89.65	13.498%	$101.751	$101.75	$101.75	$101.80
Purchase #5	$136.82	5.806%	$144.7638	$144.76	$144.75	$144.80
Purchase #6	$133.62	10.369%	$147.4751	$147.48	$147.50	$147.50
Purchase #7	$18.90	4.147%	$19.6838	$19.68	$19.70	$19.70
7 purchase totals =	$641.33		$700.5997	$700.59	$700.65	$700.70