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	$110.42	12.433%	$124.1485	$124.15	$124.15	$124.10
Purchase #2	$111.98	13.868%	$127.5094	$127.51	$127.50	$127.50
Purchase #3	$238.92	7.796%	$257.5462	$257.55	$257.55	$257.50
Purchase #4	$83.48	8.315%	$90.4214	$90.42	$90.40	$90.40
Purchase #5	$108.73	6.206%	$115.4778	$115.48	$115.50	$115.50
Purchase #6	$156.46	5.192%	$164.5834	$164.58	$164.60	$164.60
Purchase #7	$115.63	5.409%	$121.8844	$121.88	$121.90	$121.90
7 purchase totals =	$925.62		$1,001.5711	$1,001.57	$1,001.60	$1,001.50