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	$232.41	11.696%	$259.5927	$259.59	$259.60	$259.60
Purchase #2	$238.75	7.568%	$256.8186	$256.82	$256.80	$256.80
Purchase #3	$229.85	13.808%	$261.5877	$261.59	$261.60	$261.60
Purchase #4	$70.89	11.254%	$78.868	$78.87	$78.85	$78.90
Purchase #5	$54.58	11.654%	$60.9408	$60.94	$60.95	$60.90
Purchase #6	$216.80	10.341%	$239.2193	$239.22	$239.20	$239.20
Purchase #7	$146.56	3.870%	$152.2319	$152.23	$152.25	$152.20
7 purchase totals =	$1,189.84		$1,309.2590	$1,309.26	$1,309.25	$1,309.20