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	$219.35	6.741%	$234.1364	$234.14	$234.15	$234.10
Purchase #2	$45.72	3.215%	$47.1899	$47.19	$47.20	$47.20
Purchase #3	$53.80	3.221%	$55.5329	$55.53	$55.55	$55.50
Purchase #4	$24.97	10.209%	$27.5192	$27.52	$27.50	$27.50
Purchase #5	$47.42	11.446%	$52.8477	$52.85	$52.85	$52.80
Purchase #6	$200.56	5.142%	$210.8728	$210.87	$210.85	$210.90
Purchase #7	$131.42	7.400%	$141.1451	$141.15	$141.15	$141.10
7 purchase totals =	$723.24		$769.2440	$769.25	$769.25	$769.10