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	$113.41	8.798%	$123.3878	$123.39	$123.40	$123.40
Purchase #2	$131.58	4.348%	$137.3011	$137.30	$137.30	$137.30
Purchase #3	$123.44	4.362%	$128.8245	$128.82	$128.80	$128.80
Purchase #4	$96.76	13.391%	$109.7171	$109.72	$109.70	$109.70
Purchase #5	$50.81	6.135%	$53.9272	$53.93	$53.95	$53.90
Purchase #6	$73.83	10.776%	$81.7859	$81.79	$81.80	$81.80
Purchase #7	$42.38	8.251%	$45.8768	$45.88	$45.90	$45.90
7 purchase totals =	$632.21		$680.8204	$680.83	$680.85	$680.80