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	$153.85	4.109%	$160.1717	$160.17	$160.15	$160.20
Purchase #2	$65.52	4.361%	$68.3773	$68.38	$68.40	$68.40
Purchase #3	$169.77	8.494%	$184.1903	$184.19	$184.20	$184.20
Purchase #4	$90.37	3.260%	$93.3161	$93.32	$93.30	$93.30
Purchase #5	$86.44	3.184%	$89.1922	$89.19	$89.20	$89.20
Purchase #6	$90.27	13.606%	$102.5521	$102.55	$102.55	$102.60
Purchase #7	$164.37	12.847%	$185.4866	$185.49	$185.50	$185.50
7 purchase totals =	$820.59		$883.2863	$883.29	$883.30	$883.40