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	$22.56	5.787%	$23.8655	$23.87	$23.85	$23.90
Purchase #2	$29.88	10.359%	$32.9753	$32.98	$33.00	$33.00
Purchase #3	$65.91	10.424%	$72.7805	$72.78	$72.80	$72.80
Purchase #4	$216.69	7.106%	$232.088	$232.09	$232.10	$232.10
Purchase #5	$171.55	4.820%	$179.8187	$179.82	$179.80	$179.80
Purchase #6	$88.46	12.745%	$99.7342	$99.73	$99.75	$99.70
Purchase #7	$245.69	7.572%	$264.2936	$264.29	$264.30	$264.30
7 purchase totals =	$840.74		$905.5558	$905.56	$905.60	$905.60