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	$187.33	9.149%	$204.4688	$204.47	$204.45	$204.50
Purchase #2	$36.82	12.665%	$41.4833	$41.48	$41.50	$41.50
Purchase #3	$111.39	10.436%	$123.0147	$123.01	$123.00	$123.00
Purchase #4	$67.50	6.261%	$71.7262	$71.73	$71.75	$71.70
Purchase #5	$122.53	10.476%	$135.3662	$135.37	$135.35	$135.40
Purchase #6	$86.25	4.829%	$90.415	$90.42	$90.40	$90.40
Purchase #7	$190.51	10.160%	$209.8658	$209.87	$209.85	$209.90
7 purchase totals =	$802.33		$876.3400	$876.35	$876.30	$876.40