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	$159.55	4.579%	$166.8558	$166.86	$166.85	$166.90
Purchase #2	$173.67	10.479%	$191.8689	$191.87	$191.85	$191.90
Purchase #3	$249.78	4.749%	$261.6421	$261.64	$261.65	$261.60
Purchase #4	$152.90	6.326%	$162.5725	$162.57	$162.55	$162.60
Purchase #5	$92.30	4.235%	$96.2089	$96.21	$96.20	$96.20
Purchase #6	$45.83	5.284%	$48.2517	$48.25	$48.25	$48.30
Purchase #7	$83.28	3.342%	$86.0632	$86.06	$86.05	$86.10
7 purchase totals =	$957.31		$1,013.4631	$1,013.46	$1,013.40	$1,013.60