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	$214.51	10.868%	$237.8229	$237.82	$237.80	$237.80
Purchase #2	$90.37	5.779%	$95.5925	$95.59	$95.60	$95.60
Purchase #3	$48.34	4.321%	$50.4288	$50.43	$50.45	$50.40
Purchase #4	$201.42	12.228%	$226.0496	$226.05	$226.05	$226.00
Purchase #5	$64.96	6.185%	$68.9778	$68.98	$69.00	$69.00
Purchase #6	$80.94	5.423%	$85.3294	$85.33	$85.35	$85.30
Purchase #7	$55.53	7.850%	$59.8891	$59.89	$59.90	$59.90
7 purchase totals =	$756.07		$824.0901	$824.09	$824.15	$824.00