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	$145.56	11.867%	$162.8336	$162.83	$162.85	$162.80
Purchase #2	$84.50	7.602%	$90.9237	$90.92	$90.90	$90.90
Purchase #3	$247.42	4.736%	$259.1378	$259.14	$259.15	$259.10
Purchase #4	$245.64	12.339%	$275.9495	$275.95	$275.95	$275.90
Purchase #5	$243.76	12.853%	$275.0905	$275.09	$275.10	$275.10
Purchase #6	$152.89	11.542%	$170.5366	$170.54	$170.55	$170.50
Purchase #7	$215.97	4.223%	$225.0904	$225.09	$225.10	$225.10
7 purchase totals =	$1,335.74		$1,459.5621	$1,459.56	$1,459.60	$1,459.40