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	$246.78	9.560%	$270.3722	$270.37	$270.35	$270.40
Purchase #2	$37.91	11.789%	$42.3792	$42.38	$42.40	$42.40
Purchase #3	$100.39	3.784%	$104.1888	$104.19	$104.20	$104.20
Purchase #4	$71.44	12.224%	$80.1728	$80.17	$80.15	$80.20
Purchase #5	$72.37	13.192%	$81.9171	$81.92	$81.90	$81.90
Purchase #6	$80.51	12.739%	$90.7662	$90.77	$90.75	$90.80
Purchase #7	$97.56	8.407%	$105.7619	$105.76	$105.75	$105.80
7 purchase totals =	$706.96		$775.5582	$775.56	$775.50	$775.70