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	$82.84	9.698%	$90.8738	$90.87	$90.85	$90.90
Purchase #2	$32.29	3.397%	$33.3869	$33.39	$33.40	$33.40
Purchase #3	$224.34	6.180%	$238.2042	$238.20	$238.20	$238.20
Purchase #4	$43.33	4.439%	$45.2534	$45.25	$45.25	$45.30
Purchase #5	$131.73	12.368%	$148.0224	$148.02	$148.00	$148.00
Purchase #6	$6.41	3.716%	$6.6482	$6.65	$6.65	$6.60
Purchase #7	$50.30	6.142%	$53.3894	$53.39	$53.40	$53.40
7 purchase totals =	$571.24		$615.7783	$615.77	$615.75	$615.80