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	$166.98	10.440%	$184.4127	$184.41	$184.40	$184.40
Purchase #2	$81.92	10.852%	$90.81	$90.81	$90.80	$90.80
Purchase #3	$129.77	11.198%	$144.3016	$144.30	$144.30	$144.30
Purchase #4	$64.74	13.834%	$73.6961	$73.70	$73.70	$73.70
Purchase #5	$59.90	5.208%	$63.0196	$63.02	$63.00	$63.00
Purchase #6	$230.43	8.609%	$250.2677	$250.27	$250.25	$250.30
Purchase #7	$72.89	13.676%	$82.8584	$82.86	$82.85	$82.90
7 purchase totals =	$806.63		$889.3661	$889.37	$889.30	$889.40