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	$100.39	13.442%	$113.8844	$113.88	$113.90	$113.90
Purchase #2	$81.61	7.453%	$87.6924	$87.69	$87.70	$87.70
Purchase #3	$188.56	12.489%	$212.1093	$212.11	$212.10	$212.10
Purchase #4	$86.31	4.198%	$89.9333	$89.93	$89.95	$89.90
Purchase #5	$200.72	10.761%	$222.3195	$222.32	$222.30	$222.30
Purchase #6	$224.34	7.786%	$241.8071	$241.81	$241.80	$241.80
Purchase #7	$103.84	7.382%	$111.5055	$111.51	$111.50	$111.50
7 purchase totals =	$985.77		$1,079.2515	$1,079.25	$1,079.25	$1,079.20