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	$71.32	9.634%	$78.191	$78.19	$78.20	$78.20
Purchase #2	$226.72	10.534%	$250.6027	$250.60	$250.60	$250.60
Purchase #3	$118.99	10.702%	$131.7243	$131.72	$131.70	$131.70
Purchase #4	$6.97	12.478%	$7.8397	$7.84	$7.85	$7.80
Purchase #5	$90.43	6.687%	$96.4771	$96.48	$96.50	$96.50
Purchase #6	$42.99	12.330%	$48.2907	$48.29	$48.30	$48.30
Purchase #7	$64.59	8.468%	$70.0595	$70.06	$70.05	$70.10
7 purchase totals =	$622.01		$683.1850	$683.18	$683.20	$683.20