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	$17.70	4.861%	$18.5604	$18.56	$18.55	$18.60
Purchase #2	$55.56	6.768%	$59.3203	$59.32	$59.30	$59.30
Purchase #3	$45.28	13.366%	$51.3321	$51.33	$51.35	$51.30
Purchase #4	$49.80	7.585%	$53.5773	$53.58	$53.60	$53.60
Purchase #5	$227.75	8.781%	$247.7487	$247.75	$247.75	$247.70
Purchase #6	$216.75	5.349%	$228.344	$228.34	$228.35	$228.30
Purchase #7	$102.96	8.118%	$111.3183	$111.32	$111.30	$111.30
7 purchase totals =	$715.80		$770.2011	$770.20	$770.20	$770.10