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	$30.96	6.804%	$33.0665	$33.07	$33.05	$33.10
Purchase #2	$128.42	11.240%	$142.8544	$142.85	$142.85	$142.90
Purchase #3	$67.76	12.658%	$76.3371	$76.34	$76.35	$76.30
Purchase #4	$65.46	10.791%	$72.5238	$72.52	$72.50	$72.50
Purchase #5	$75.98	11.372%	$84.6204	$84.62	$84.60	$84.60
Purchase #6	$205.85	8.245%	$222.8223	$222.82	$222.80	$222.80
Purchase #7	$165.95	5.617%	$175.2714	$175.27	$175.25	$175.30
7 purchase totals =	$740.38		$807.4959	$807.49	$807.40	$807.50