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	$163.71	5.607%	$172.8892	$172.89	$172.90	$172.90
Purchase #2	$126.94	9.602%	$139.1288	$139.13	$139.15	$139.10
Purchase #3	$28.87	8.213%	$31.2411	$31.24	$31.25	$31.20
Purchase #4	$55.62	9.444%	$60.8728	$60.87	$60.85	$60.90
Purchase #5	$152.52	10.751%	$168.9174	$168.92	$168.90	$168.90
Purchase #6	$141.74	7.846%	$152.8609	$152.86	$152.85	$152.90
Purchase #7	$180.99	3.282%	$186.9301	$186.93	$186.95	$186.90
7 purchase totals =	$850.39		$912.8403	$912.84	$912.85	$912.80