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	$233.83	8.379%	$253.4226	$253.42	$253.40	$253.40
Purchase #2	$165.43	4.271%	$172.4955	$172.50	$172.50	$172.50
Purchase #3	$38.67	9.454%	$42.3259	$42.33	$42.35	$42.30
Purchase #4	$152.95	10.517%	$169.0358	$169.04	$169.05	$169.00
Purchase #5	$28.80	8.574%	$31.2693	$31.27	$31.25	$31.30
Purchase #6	$176.77	12.226%	$198.3819	$198.38	$198.40	$198.40
Purchase #7	$54.97	11.378%	$61.2245	$61.22	$61.20	$61.20
7 purchase totals =	$851.42		$928.1555	$928.16	$928.15	$928.10