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	$75.48	3.759%	$78.3173	$78.32	$78.30	$78.30
Purchase #2	$138.32	9.313%	$151.2017	$151.20	$151.20	$151.20
Purchase #3	$246.33	3.559%	$255.0969	$255.10	$255.10	$255.10
Purchase #4	$143.80	7.457%	$154.5232	$154.52	$154.50	$154.50
Purchase #5	$88.79	5.760%	$93.9043	$93.90	$93.90	$93.90
Purchase #6	$189.95	13.286%	$215.1868	$215.19	$215.20	$215.20
Purchase #7	$216.88	6.551%	$231.0878	$231.09	$231.10	$231.10
7 purchase totals =	$1,099.55		$1,179.3180	$1,179.32	$1,179.30	$1,179.30