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	$239.39	12.128%	$268.4232	$268.42	$268.40	$268.40
Purchase #2	$152.97	10.152%	$168.4995	$168.50	$168.50	$168.50
Purchase #3	$18.91	9.314%	$20.6713	$20.67	$20.65	$20.70
Purchase #4	$181.87	7.518%	$195.543	$195.54	$195.55	$195.50
Purchase #5	$119.66	3.148%	$123.4269	$123.43	$123.45	$123.40
Purchase #6	$90.34	9.821%	$99.2123	$99.21	$99.20	$99.20
Purchase #7	$154.90	7.134%	$165.9506	$165.95	$165.95	$166.00
7 purchase totals =	$958.04		$1,041.7268	$1,041.72	$1,041.70	$1,041.70