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	$67.79	6.213%	$72.0018	$72.00	$72.00	$72.00
Purchase #2	$117.27	10.866%	$130.0126	$130.01	$130.00	$130.00
Purchase #3	$163.54	4.588%	$171.0432	$171.04	$171.05	$171.00
Purchase #4	$150.54	13.170%	$170.3661	$170.37	$170.35	$170.40
Purchase #5	$37.27	3.355%	$38.5204	$38.52	$38.50	$38.50
Purchase #6	$226.92	5.833%	$240.1562	$240.16	$240.15	$240.20
Purchase #7	$152.47	11.858%	$170.5499	$170.55	$170.55	$170.50
7 purchase totals =	$915.80		$992.6502	$992.65	$992.60	$992.60