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	$123.61	12.109%	$138.5779	$138.58	$138.60	$138.60
Purchase #2	$142.27	11.158%	$158.1445	$158.14	$158.15	$158.10
Purchase #3	$89.89	7.282%	$96.4358	$96.44	$96.45	$96.40
Purchase #4	$48.75	6.327%	$51.8344	$51.83	$51.85	$51.80
Purchase #5	$223.33	8.703%	$242.7664	$242.77	$242.75	$242.80
Purchase #6	$132.67	13.579%	$150.6853	$150.69	$150.70	$150.70
Purchase #7	$84.43	5.470%	$89.0483	$89.05	$89.05	$89.00
7 purchase totals =	$844.95		$927.4926	$927.50	$927.55	$927.40