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	$240.32	7.487%	$258.3128	$258.31	$258.30	$258.30
Purchase #2	$169.41	9.407%	$185.3464	$185.35	$185.35	$185.30
Purchase #3	$155.77	10.369%	$171.9218	$171.92	$171.90	$171.90
Purchase #4	$10.51	4.407%	$10.9732	$10.97	$10.95	$11.00
Purchase #5	$238.49	3.364%	$246.5128	$246.51	$246.50	$246.50
Purchase #6	$143.71	5.712%	$151.9187	$151.92	$151.90	$151.90
Purchase #7	$146.33	5.783%	$154.7923	$154.79	$154.80	$154.80
7 purchase totals =	$1,104.54		$1,179.7780	$1,179.77	$1,179.70	$1,179.70