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	$126.72	3.379%	$131.0019	$131.00	$131.00	$131.00
Purchase #2	$172.62	4.121%	$179.7337	$179.73	$179.75	$179.70
Purchase #3	$45.37	7.663%	$48.8467	$48.85	$48.85	$48.80
Purchase #4	$42.57	7.181%	$45.627	$45.63	$45.65	$45.60
Purchase #5	$140.25	10.374%	$154.7995	$154.80	$154.80	$154.80
Purchase #6	$187.28	11.804%	$209.3865	$209.39	$209.40	$209.40
Purchase #7	$18.47	8.292%	$20.0015	$20.00	$20.00	$20.00
7 purchase totals =	$733.28		$789.3968	$789.40	$789.45	$789.30