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	$89.85	12.167%	$100.782	$100.78	$100.80	$100.80
Purchase #2	$238.72	10.419%	$263.5922	$263.59	$263.60	$263.60
Purchase #3	$162.52	3.203%	$167.7255	$167.73	$167.75	$167.70
Purchase #4	$176.33	5.342%	$185.7495	$185.75	$185.75	$185.70
Purchase #5	$140.89	10.769%	$156.0624	$156.06	$156.05	$156.10
Purchase #6	$228.42	4.532%	$238.772	$238.77	$238.75	$238.80
Purchase #7	$204.64	3.800%	$212.4163	$212.42	$212.40	$212.40
7 purchase totals =	$1,241.37		$1,325.0999	$1,325.10	$1,325.10	$1,325.10