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	$133.67	6.608%	$142.5029	$142.50	$142.50	$142.50
Purchase #2	$84.25	12.300%	$94.6128	$94.61	$94.60	$94.60
Purchase #3	$204.25	12.384%	$229.5443	$229.54	$229.55	$229.50
Purchase #4	$100.29	11.279%	$111.6017	$111.60	$111.60	$111.60
Purchase #5	$75.49	9.516%	$82.6736	$82.67	$82.65	$82.70
Purchase #6	$50.65	10.320%	$55.8771	$55.88	$55.90	$55.90
Purchase #7	$170.77	7.272%	$183.1884	$183.19	$183.20	$183.20
7 purchase totals =	$819.37		$900.0008	$899.99	$900.00	$900.00