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	$84.51	7.223%	$90.6142	$90.61	$90.60	$90.60
Purchase #2	$239.61	8.599%	$260.2141	$260.21	$260.20	$260.20
Purchase #3	$88.30	8.803%	$96.073	$96.07	$96.05	$96.10
Purchase #4	$74.53	11.519%	$83.1151	$83.12	$83.10	$83.10
Purchase #5	$88.60	5.594%	$93.5563	$93.56	$93.55	$93.60
Purchase #6	$168.31	7.703%	$181.2749	$181.27	$181.25	$181.30
Purchase #7	$158.90	9.118%	$173.3885	$173.39	$173.40	$173.40
7 purchase totals =	$902.76		$978.2361	$978.23	$978.15	$978.30