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	$28.61	13.201%	$32.3868	$32.39	$32.40	$32.40
Purchase #2	$228.96	6.528%	$243.9065	$243.91	$243.90	$243.90
Purchase #3	$151.69	11.468%	$169.0858	$169.09	$169.10	$169.10
Purchase #4	$240.31	10.540%	$265.6387	$265.64	$265.65	$265.60
Purchase #5	$95.62	3.637%	$99.0977	$99.10	$99.10	$99.10
Purchase #6	$112.38	12.380%	$126.2926	$126.29	$126.30	$126.30
Purchase #7	$112.47	9.423%	$123.068	$123.07	$123.05	$123.10
7 purchase totals =	$970.04		$1,059.4761	$1,059.49	$1,059.50	$1,059.50