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	$127.86	6.534%	$136.2144	$136.21	$136.20	$136.20
Purchase #2	$154.31	8.458%	$167.3615	$167.36	$167.35	$167.40
Purchase #3	$202.82	8.380%	$219.8163	$219.82	$219.80	$219.80
Purchase #4	$184.54	13.163%	$208.831	$208.83	$208.85	$208.80
Purchase #5	$148.84	6.765%	$158.909	$158.91	$158.90	$158.90
Purchase #6	$95.48	4.443%	$99.7222	$99.72	$99.70	$99.70
Purchase #7	$192.38	9.131%	$209.9462	$209.95	$209.95	$209.90
7 purchase totals =	$1,106.23		$1,200.8006	$1,200.80	$1,200.75	$1,200.70