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	$100.48	4.638%	$105.1403	$105.14	$105.15	$105.10
Purchase #2	$249.34	8.614%	$270.8181	$270.82	$270.80	$270.80
Purchase #3	$105.75	8.163%	$114.3824	$114.38	$114.40	$114.40
Purchase #4	$172.53	13.781%	$196.3064	$196.31	$196.30	$196.30
Purchase #5	$123.59	6.241%	$131.3033	$131.30	$131.30	$131.30
Purchase #6	$170.92	6.532%	$182.0845	$182.08	$182.10	$182.10
Purchase #7	$205.40	6.858%	$219.4863	$219.49	$219.50	$219.50
7 purchase totals =	$1,128.01		$1,219.5213	$1,219.52	$1,219.55	$1,219.50