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	$80.38	5.829%	$85.0654	$85.07	$85.05	$85.10
Purchase #2	$152.25	6.667%	$162.4005	$162.40	$162.40	$162.40
Purchase #3	$211.43	10.102%	$232.7887	$232.79	$232.80	$232.80
Purchase #4	$33.79	13.756%	$38.4382	$38.44	$38.45	$38.40
Purchase #5	$17.75	6.281%	$18.8649	$18.86	$18.85	$18.90
Purchase #6	$72.59	11.328%	$80.813	$80.81	$80.80	$80.80
Purchase #7	$40.43	13.666%	$45.9552	$45.96	$45.95	$46.00
7 purchase totals =	$608.62		$664.3259	$664.33	$664.30	$664.40