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	$131.29	5.155%	$138.058	$138.06	$138.05	$138.10
Purchase #2	$144.59	12.618%	$162.8344	$162.83	$162.85	$162.80
Purchase #3	$145.65	11.762%	$162.7814	$162.78	$162.80	$162.80
Purchase #4	$185.93	10.260%	$205.0064	$205.01	$205.00	$205.00
Purchase #5	$110.84	4.790%	$116.1492	$116.15	$116.15	$116.10
Purchase #6	$60.56	11.223%	$67.3566	$67.36	$67.35	$67.40
Purchase #7	$110.49	12.777%	$124.6073	$124.61	$124.60	$124.60
7 purchase totals =	$889.35		$976.7933	$976.80	$976.80	$976.80