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	$162.34	11.833%	$181.5497	$181.55	$181.55	$181.50
Purchase #2	$94.64	4.256%	$98.6679	$98.67	$98.65	$98.70
Purchase #3	$220.25	8.258%	$238.4382	$238.44	$238.45	$238.40
Purchase #4	$24.92	6.408%	$26.5169	$26.52	$26.50	$26.50
Purchase #5	$45.31	10.452%	$50.0458	$50.05	$50.05	$50.00
Purchase #6	$76.40	7.524%	$82.1483	$82.15	$82.15	$82.10
Purchase #7	$97.40	9.743%	$106.8897	$106.89	$106.90	$106.90
7 purchase totals =	$721.26		$784.2565	$784.27	$784.25	$784.10