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	$98.52	9.778%	$108.1533	$108.15	$108.15	$108.20
Purchase #2	$41.96	5.118%	$44.1075	$44.11	$44.10	$44.10
Purchase #3	$246.49	9.751%	$270.5252	$270.53	$270.55	$270.50
Purchase #4	$98.90	12.319%	$111.0835	$111.08	$111.10	$111.10
Purchase #5	$241.64	7.242%	$259.1396	$259.14	$259.15	$259.10
Purchase #6	$117.36	12.864%	$132.4572	$132.46	$132.45	$132.50
Purchase #7	$145.41	9.764%	$159.6078	$159.61	$159.60	$159.60
7 purchase totals =	$990.28		$1,085.0741	$1,085.08	$1,085.10	$1,085.10