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	$123.29	11.731%	$137.7531	$137.75	$137.75	$137.80
Purchase #2	$87.57	3.253%	$90.4187	$90.42	$90.40	$90.40
Purchase #3	$130.82	4.733%	$137.0117	$137.01	$137.00	$137.00
Purchase #4	$213.46	7.211%	$228.8526	$228.85	$228.85	$228.90
Purchase #5	$83.82	11.449%	$93.4166	$93.42	$93.40	$93.40
Purchase #6	$55.67	6.397%	$59.2312	$59.23	$59.25	$59.20
Purchase #7	$202.91	4.137%	$211.3044	$211.30	$211.30	$211.30
7 purchase totals =	$897.54		$957.9883	$957.98	$957.95	$958.00