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	$159.97	3.697%	$165.8841	$165.88	$165.90	$165.90
Purchase #2	$120.56	5.765%	$127.5103	$127.51	$127.50	$127.50
Purchase #3	$72.37	8.874%	$78.7921	$78.79	$78.80	$78.80
Purchase #4	$233.48	11.237%	$259.7161	$259.72	$259.70	$259.70
Purchase #5	$29.33	10.741%	$32.4803	$32.48	$32.50	$32.50
Purchase #6	$195.96	9.459%	$214.4959	$214.50	$214.50	$214.50
Purchase #7	$28.37	12.364%	$31.8777	$31.88	$31.90	$31.90
7 purchase totals =	$840.04		$910.7565	$910.76	$910.80	$910.80