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	$123.71	5.796%	$130.8802	$130.88	$130.90	$130.90
Purchase #2	$213.29	13.104%	$241.2395	$241.24	$241.25	$241.20
Purchase #3	$181.38	3.158%	$187.108	$187.11	$187.10	$187.10
Purchase #4	$135.73	6.701%	$144.8253	$144.83	$144.85	$144.80
Purchase #5	$181.96	11.837%	$203.4986	$203.50	$203.50	$203.50
Purchase #6	$64.38	11.246%	$71.6202	$71.62	$71.60	$71.60
Purchase #7	$113.26	11.758%	$126.5771	$126.58	$126.60	$126.60
7 purchase totals =	$1,013.71		$1,105.7489	$1,105.76	$1,105.80	$1,105.70