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	$245.55	12.442%	$276.1013	$276.10	$276.10	$276.10
Purchase #2	$44.34	3.161%	$45.7416	$45.74	$45.75	$45.70
Purchase #3	$199.91	5.146%	$210.1974	$210.20	$210.20	$210.20
Purchase #4	$192.28	11.544%	$214.4768	$214.48	$214.50	$214.50
Purchase #5	$125.50	11.215%	$139.5748	$139.57	$139.55	$139.60
Purchase #6	$95.75	4.554%	$100.1105	$100.11	$100.10	$100.10
Purchase #7	$107.86	8.373%	$116.8911	$116.89	$116.90	$116.90
7 purchase totals =	$1,011.19		$1,103.0935	$1,103.09	$1,103.10	$1,103.10