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	$28.52	12.656%	$32.1295	$32.13	$32.15	$32.10
Purchase #2	$121.86	7.791%	$131.3541	$131.35	$131.35	$131.40
Purchase #3	$90.64	7.113%	$97.0872	$97.09	$97.10	$97.10
Purchase #4	$41.29	3.846%	$42.878	$42.88	$42.90	$42.90
Purchase #5	$150.93	10.644%	$166.995	$167.00	$167.00	$167.00
Purchase #6	$144.59	13.661%	$164.3424	$164.34	$164.35	$164.30
Purchase #7	$129.59	12.484%	$145.768	$145.77	$145.75	$145.80
7 purchase totals =	$707.42		$780.5542	$780.56	$780.60	$780.60