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	$125.54	10.578%	$138.8196	$138.82	$138.80	$138.80
Purchase #2	$82.64	8.205%	$89.4206	$89.42	$89.40	$89.40
Purchase #3	$116.72	10.457%	$128.9254	$128.93	$128.95	$128.90
Purchase #4	$190.65	3.550%	$197.4181	$197.42	$197.40	$197.40
Purchase #5	$36.28	13.856%	$41.307	$41.31	$41.30	$41.30
Purchase #6	$55.49	7.848%	$59.8449	$59.84	$59.85	$59.80
Purchase #7	$35.31	4.308%	$36.8312	$36.83	$36.85	$36.80
7 purchase totals =	$642.63		$692.5668	$692.57	$692.55	$692.40