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	$40.91	3.596%	$42.3811	$42.38	$42.40	$42.40
Purchase #2	$154.58	11.605%	$172.519	$172.52	$172.50	$172.50
Purchase #3	$67.89	5.228%	$71.4393	$71.44	$71.45	$71.40
Purchase #4	$211.51	7.854%	$228.122	$228.12	$228.10	$228.10
Purchase #5	$144.72	13.714%	$164.5669	$164.57	$164.55	$164.60
Purchase #6	$233.27	3.578%	$241.6164	$241.62	$241.60	$241.60
Purchase #7	$226.56	4.213%	$236.105	$236.11	$236.10	$236.10
7 purchase totals =	$1,079.44		$1,156.7497	$1,156.76	$1,156.70	$1,156.70