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	$163.34	13.606%	$185.564	$185.56	$185.55	$185.60
Purchase #2	$132.30	3.790%	$137.3142	$137.31	$137.30	$137.30
Purchase #3	$105.89	5.342%	$111.5466	$111.55	$111.55	$111.50
Purchase #4	$121.39	8.786%	$132.0553	$132.06	$132.05	$132.10
Purchase #5	$204.86	8.448%	$222.1666	$222.17	$222.15	$222.20
Purchase #6	$244.96	11.160%	$272.2975	$272.30	$272.30	$272.30
Purchase #7	$215.26	8.618%	$233.8111	$233.81	$233.80	$233.80
7 purchase totals =	$1,188.00		$1,294.7553	$1,294.76	$1,294.70	$1,294.80