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	$232.92	9.172%	$254.2834	$254.28	$254.30	$254.30
Purchase #2	$249.69	5.653%	$263.805	$263.81	$263.80	$263.80
Purchase #3	$67.57	3.762%	$70.112	$70.11	$70.10	$70.10
Purchase #4	$250.28	4.277%	$260.9845	$260.98	$261.00	$261.00
Purchase #5	$115.78	6.260%	$123.0278	$123.03	$123.05	$123.00
Purchase #6	$121.61	4.449%	$127.0204	$127.02	$127.00	$127.00
Purchase #7	$183.76	7.158%	$196.9135	$196.91	$196.90	$196.90
7 purchase totals =	$1,221.61		$1,296.1466	$1,296.14	$1,296.15	$1,296.10