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	$138.56	6.197%	$147.1466	$147.15	$147.15	$147.10
Purchase #2	$224.76	8.376%	$243.5859	$243.59	$243.60	$243.60
Purchase #3	$60.77	12.346%	$68.2727	$68.27	$68.25	$68.30
Purchase #4	$217.61	11.140%	$241.8518	$241.85	$241.85	$241.90
Purchase #5	$92.50	4.797%	$96.9372	$96.94	$96.95	$96.90
Purchase #6	$73.86	3.588%	$76.5101	$76.51	$76.50	$76.50
Purchase #7	$38.79	4.606%	$40.5767	$40.58	$40.60	$40.60
7 purchase totals =	$846.85		$914.8810	$914.89	$914.90	$914.90