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	$173.32	6.476%	$184.5442	$184.54	$184.55	$184.50
Purchase #2	$232.50	11.615%	$259.5049	$259.50	$259.50	$259.50
Purchase #3	$175.33	10.584%	$193.8869	$193.89	$193.90	$193.90
Purchase #4	$182.89	12.421%	$205.6068	$205.61	$205.60	$205.60
Purchase #5	$8.68	10.124%	$9.5588	$9.56	$9.55	$9.60
Purchase #6	$126.33	9.182%	$137.9296	$137.93	$137.95	$137.90
Purchase #7	$99.58	9.601%	$109.1407	$109.14	$109.15	$109.10
7 purchase totals =	$998.63		$1,100.1719	$1,100.17	$1,100.20	$1,100.10