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	$186.59	6.815%	$199.3061	$199.31	$199.30	$199.30
Purchase #2	$81.78	8.759%	$88.9431	$88.94	$88.95	$88.90
Purchase #3	$104.81	6.716%	$111.849	$111.85	$111.85	$111.80
Purchase #4	$175.63	9.753%	$192.7592	$192.76	$192.75	$192.80
Purchase #5	$90.66	10.810%	$100.4603	$100.46	$100.45	$100.50
Purchase #6	$27.36	13.768%	$31.1269	$31.13	$31.15	$31.10
Purchase #7	$236.46	5.659%	$249.8413	$249.84	$249.85	$249.80
7 purchase totals =	$903.29		$974.2859	$974.29	$974.30	$974.20