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	$242.46	3.586%	$251.1546	$251.15	$251.15	$251.20
Purchase #2	$79.49	7.515%	$85.4637	$85.46	$85.45	$85.50
Purchase #3	$201.45	4.643%	$210.8033	$210.80	$210.80	$210.80
Purchase #4	$242.87	12.487%	$273.1972	$273.20	$273.20	$273.20
Purchase #5	$151.66	7.690%	$163.3227	$163.32	$163.30	$163.30
Purchase #6	$90.50	9.770%	$99.3419	$99.34	$99.35	$99.30
Purchase #7	$100.52	12.339%	$112.9232	$112.92	$112.90	$112.90
7 purchase totals =	$1,108.95		$1,196.2066	$1,196.19	$1,196.15	$1,196.20