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	$42.57	11.132%	$47.3089	$47.31	$47.30	$47.30
Purchase #2	$221.42	3.699%	$229.6103	$229.61	$229.60	$229.60
Purchase #3	$176.55	4.678%	$184.809	$184.81	$184.80	$184.80
Purchase #4	$88.86	13.365%	$100.7361	$100.74	$100.75	$100.70
Purchase #5	$75.50	9.172%	$82.4249	$82.42	$82.40	$82.40
Purchase #6	$210.58	6.645%	$224.573	$224.57	$224.55	$224.60
Purchase #7	$135.56	9.756%	$148.7852	$148.79	$148.80	$148.80
7 purchase totals =	$951.04		$1,018.2474	$1,018.25	$1,018.20	$1,018.20