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	$157.49	13.280%	$178.4047	$178.40	$178.40	$178.40
Purchase #2	$149.45	13.786%	$170.0532	$170.05	$170.05	$170.10
Purchase #3	$73.59	6.274%	$78.207	$78.21	$78.20	$78.20
Purchase #4	$42.35	9.180%	$46.2377	$46.24	$46.25	$46.20
Purchase #5	$102.58	8.476%	$111.2747	$111.27	$111.25	$111.30
Purchase #6	$90.56	13.641%	$102.9133	$102.91	$102.90	$102.90
Purchase #7	$70.96	3.350%	$73.3372	$73.34	$73.35	$73.30
7 purchase totals =	$686.98		$760.4278	$760.42	$760.40	$760.40