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	$71.72	11.847%	$80.2167	$80.22	$80.20	$80.20
Purchase #2	$65.55	9.531%	$71.7976	$71.80	$71.80	$71.80
Purchase #3	$156.99	4.653%	$164.2947	$164.29	$164.30	$164.30
Purchase #4	$75.49	9.409%	$82.5929	$82.59	$82.60	$82.60
Purchase #5	$41.29	11.670%	$46.1085	$46.11	$46.10	$46.10
Purchase #6	$45.55	4.812%	$47.7419	$47.74	$47.75	$47.70
Purchase #7	$170.38	12.627%	$191.8939	$191.89	$191.90	$191.90
7 purchase totals =	$626.97		$684.6462	$684.64	$684.65	$684.60