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	$207.57	5.210%	$218.3844	$218.38	$218.40	$218.40
Purchase #2	$208.56	11.758%	$233.0825	$233.08	$233.10	$233.10
Purchase #3	$199.94	7.542%	$215.0195	$215.02	$215.00	$215.00
Purchase #4	$92.68	7.841%	$99.947	$99.95	$99.95	$99.90
Purchase #5	$172.87	5.570%	$182.4989	$182.50	$182.50	$182.50
Purchase #6	$37.96	12.223%	$42.5999	$42.60	$42.60	$42.60
Purchase #7	$166.25	10.261%	$183.3089	$183.31	$183.30	$183.30
7 purchase totals =	$1,085.83		$1,174.8411	$1,174.84	$1,174.85	$1,174.80