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	$18.27	8.759%	$19.8703	$19.87	$19.85	$19.90
Purchase #2	$242.55	11.464%	$270.3559	$270.36	$270.35	$270.40
Purchase #3	$102.33	12.154%	$114.7672	$114.77	$114.75	$114.80
Purchase #4	$246.85	7.320%	$264.9194	$264.92	$264.90	$264.90
Purchase #5	$55.81	6.751%	$59.5777	$59.58	$59.60	$59.60
Purchase #6	$132.64	6.810%	$141.6728	$141.67	$141.65	$141.70
Purchase #7	$98.49	7.244%	$105.6246	$105.62	$105.60	$105.60
7 purchase totals =	$896.94		$976.7879	$976.79	$976.70	$976.90