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	$250.99	3.133%	$258.8535	$258.85	$258.85	$258.90
Purchase #2	$40.41	13.258%	$45.7676	$45.77	$45.75	$45.80
Purchase #3	$29.39	7.698%	$31.6524	$31.65	$31.65	$31.70
Purchase #4	$46.80	9.290%	$51.1477	$51.15	$51.15	$51.10
Purchase #5	$106.88	10.364%	$117.957	$117.96	$117.95	$118.00
Purchase #6	$84.40	7.639%	$90.8473	$90.85	$90.85	$90.80
Purchase #7	$82.51	10.540%	$91.2066	$91.21	$91.20	$91.20
7 purchase totals =	$641.38		$687.4321	$687.44	$687.40	$687.50