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	$159.46	8.183%	$172.5086	$172.51	$172.50	$172.50
Purchase #2	$218.60	9.615%	$239.6184	$239.62	$239.60	$239.60
Purchase #3	$80.41	12.368%	$90.3551	$90.36	$90.35	$90.40
Purchase #4	$198.73	12.182%	$222.9393	$222.94	$222.95	$222.90
Purchase #5	$246.43	8.725%	$267.931	$267.93	$267.95	$267.90
Purchase #6	$208.25	4.412%	$217.438	$217.44	$217.45	$217.40
Purchase #7	$50.78	4.181%	$52.9031	$52.90	$52.90	$52.90
7 purchase totals =	$1,162.66		$1,263.6935	$1,263.70	$1,263.70	$1,263.60