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	$218.31	11.114%	$242.573	$242.57	$242.55	$242.60
Purchase #2	$155.58	3.233%	$160.6099	$160.61	$160.60	$160.60
Purchase #3	$194.92	4.248%	$203.2002	$203.20	$203.20	$203.20
Purchase #4	$7.83	9.620%	$8.5832	$8.58	$8.60	$8.60
Purchase #5	$63.44	13.559%	$72.0418	$72.04	$72.05	$72.00
Purchase #6	$199.71	11.460%	$222.5968	$222.60	$222.60	$222.60
Purchase #7	$85.37	3.385%	$88.2598	$88.26	$88.25	$88.30
7 purchase totals =	$925.16		$997.8647	$997.86	$997.85	$997.90