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	$238.59	13.393%	$270.5444	$270.54	$270.55	$270.50
Purchase #2	$80.55	13.233%	$91.2092	$91.21	$91.20	$91.20
Purchase #3	$108.37	11.543%	$120.8791	$120.88	$120.90	$120.90
Purchase #4	$30.60	13.129%	$34.6175	$34.62	$34.60	$34.60
Purchase #5	$95.37	5.429%	$100.5476	$100.55	$100.55	$100.50
Purchase #6	$6.49	13.517%	$7.3673	$7.37	$7.35	$7.40
Purchase #7	$168.89	6.750%	$180.2901	$180.29	$180.30	$180.30
7 purchase totals =	$728.86		$805.4552	$805.46	$805.45	$805.40