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	$67.82	4.782%	$71.0632	$71.06	$71.05	$71.10
Purchase #2	$18.54	7.776%	$19.9817	$19.98	$20.00	$20.00
Purchase #3	$246.66	4.274%	$257.2022	$257.20	$257.20	$257.20
Purchase #4	$49.77	11.778%	$55.6319	$55.63	$55.65	$55.60
Purchase #5	$46.62	8.555%	$50.6083	$50.61	$50.60	$50.60
Purchase #6	$103.79	5.612%	$109.6147	$109.61	$109.60	$109.60
Purchase #7	$90.42	12.117%	$101.3762	$101.38	$101.40	$101.40
7 purchase totals =	$623.62		$665.4782	$665.47	$665.50	$665.50