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	$14.87	4.775%	$15.58	$15.58	$15.60	$15.60
Purchase #2	$227.83	7.843%	$245.6987	$245.70	$245.70	$245.70
Purchase #3	$117.60	5.288%	$123.8187	$123.82	$123.80	$123.80
Purchase #4	$94.34	5.229%	$99.273	$99.27	$99.25	$99.30
Purchase #5	$223.80	9.431%	$244.9066	$244.91	$244.90	$244.90
Purchase #6	$195.27	6.855%	$208.6558	$208.66	$208.65	$208.70
Purchase #7	$58.26	11.636%	$65.0391	$65.04	$65.05	$65.00
7 purchase totals =	$931.97		$1,002.9719	$1,002.98	$1,002.95	$1,003.00