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	$35.90	6.155%	$38.1096	$38.11	$38.10	$38.10
Purchase #2	$104.97	13.859%	$119.5178	$119.52	$119.50	$119.50
Purchase #3	$164.83	11.156%	$183.2184	$183.22	$183.20	$183.20
Purchase #4	$231.61	7.468%	$248.9066	$248.91	$248.90	$248.90
Purchase #5	$7.28	12.794%	$8.2114	$8.21	$8.20	$8.20
Purchase #6	$122.91	13.193%	$139.1255	$139.13	$139.15	$139.10
Purchase #7	$73.90	6.281%	$78.5417	$78.54	$78.55	$78.50
7 purchase totals =	$741.40		$815.6310	$815.64	$815.60	$815.50