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	$85.31	10.789%	$94.5141	$94.51	$94.50	$94.50
Purchase #2	$97.47	9.650%	$106.8759	$106.88	$106.90	$106.90
Purchase #3	$158.71	4.521%	$165.8853	$165.89	$165.90	$165.90
Purchase #4	$130.89	10.220%	$144.267	$144.27	$144.25	$144.30
Purchase #5	$126.71	11.579%	$141.3818	$141.38	$141.40	$141.40
Purchase #6	$72.28	3.157%	$74.5619	$74.56	$74.55	$74.60
Purchase #7	$236.90	5.660%	$250.3085	$250.31	$250.30	$250.30
7 purchase totals =	$908.27		$977.7945	$977.80	$977.80	$977.90