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	$24.32	10.423%	$26.8549	$26.85	$26.85	$26.90
Purchase #2	$56.61	8.616%	$61.4875	$61.49	$61.50	$61.50
Purchase #3	$65.44	10.274%	$72.1633	$72.16	$72.15	$72.20
Purchase #4	$192.76	10.262%	$212.541	$212.54	$212.55	$212.50
Purchase #5	$28.59	4.170%	$29.7822	$29.78	$29.80	$29.80
Purchase #6	$163.77	9.783%	$179.7916	$179.79	$179.80	$179.80
Purchase #7	$53.67	10.868%	$59.5029	$59.50	$59.50	$59.50
7 purchase totals =	$585.16		$642.1234	$642.11	$642.15	$642.20