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	$18.79	9.212%	$20.5209	$20.52	$20.50	$20.50
Purchase #2	$75.89	9.512%	$83.1087	$83.11	$83.10	$83.10
Purchase #3	$174.51	6.517%	$185.8828	$185.88	$185.90	$185.90
Purchase #4	$158.48	8.853%	$172.5102	$172.51	$172.50	$172.50
Purchase #5	$63.38	11.155%	$70.45	$70.45	$70.45	$70.50
Purchase #6	$30.81	9.289%	$33.6719	$33.67	$33.65	$33.70
Purchase #7	$198.60	6.570%	$211.648	$211.65	$211.65	$211.60
7 purchase totals =	$720.46		$777.7925	$777.79	$777.75	$777.80