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	$135.98	12.684%	$153.2277	$153.23	$153.25	$153.20
Purchase #2	$71.83	7.620%	$77.3034	$77.30	$77.30	$77.30
Purchase #3	$248.69	12.201%	$279.0327	$279.03	$279.05	$279.00
Purchase #4	$131.79	9.471%	$144.2718	$144.27	$144.25	$144.30
Purchase #5	$11.40	13.227%	$12.9079	$12.91	$12.90	$12.90
Purchase #6	$132.34	3.318%	$136.731	$136.73	$136.75	$136.70
Purchase #7	$55.89	5.669%	$59.0584	$59.06	$59.05	$59.10
7 purchase totals =	$787.92		$862.5329	$862.53	$862.55	$862.50