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	$163.73	10.318%	$180.6237	$180.62	$180.60	$180.60
Purchase #2	$37.32	11.140%	$41.4774	$41.48	$41.50	$41.50
Purchase #3	$242.91	6.787%	$259.3963	$259.40	$259.40	$259.40
Purchase #4	$87.54	13.480%	$99.3404	$99.34	$99.35	$99.30
Purchase #5	$65.35	7.503%	$70.2532	$70.25	$70.25	$70.30
Purchase #6	$65.27	12.822%	$73.6389	$73.64	$73.65	$73.60
Purchase #7	$140.42	3.574%	$145.4386	$145.44	$145.45	$145.40
7 purchase totals =	$802.54		$870.1685	$870.17	$870.20	$870.10