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	$113.34	12.789%	$127.8351	$127.84	$127.85	$127.80
Purchase #2	$60.30	8.855%	$65.6396	$65.64	$65.65	$65.60
Purchase #3	$6.35	5.327%	$6.6883	$6.69	$6.70	$6.70
Purchase #4	$175.85	9.122%	$191.891	$191.89	$191.90	$191.90
Purchase #5	$162.48	5.370%	$171.2052	$171.21	$171.20	$171.20
Purchase #6	$130.32	5.368%	$137.3156	$137.32	$137.30	$137.30
Purchase #7	$155.95	5.230%	$164.1062	$164.11	$164.10	$164.10
7 purchase totals =	$804.59		$864.6810	$864.70	$864.70	$864.60