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	$60.81	7.393%	$65.3057	$65.31	$65.30	$65.30
Purchase #2	$67.46	4.678%	$70.6158	$70.62	$70.60	$70.60
Purchase #3	$187.67	12.343%	$210.8341	$210.83	$210.85	$210.80
Purchase #4	$86.72	8.613%	$94.1892	$94.19	$94.20	$94.20
Purchase #5	$164.83	12.589%	$185.5804	$185.58	$185.60	$185.60
Purchase #6	$139.82	4.556%	$146.1902	$146.19	$146.20	$146.20
Purchase #7	$96.31	12.690%	$108.5317	$108.53	$108.55	$108.50
7 purchase totals =	$803.62		$881.2471	$881.25	$881.30	$881.20