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	$58.96	13.703%	$67.0393	$67.04	$67.05	$67.00
Purchase #2	$145.29	9.840%	$159.5865	$159.59	$159.60	$159.60
Purchase #3	$219.58	8.409%	$238.0445	$238.04	$238.05	$238.00
Purchase #4	$71.96	8.838%	$78.3198	$78.32	$78.30	$78.30
Purchase #5	$153.41	4.590%	$160.4515	$160.45	$160.45	$160.50
Purchase #6	$129.81	12.862%	$146.5062	$146.51	$146.50	$146.50
Purchase #7	$124.41	10.328%	$137.2591	$137.26	$137.25	$137.30
7 purchase totals =	$903.42		$987.2069	$987.21	$987.20	$987.20