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	$71.52	8.350%	$77.4919	$77.49	$77.50	$77.50
Purchase #2	$125.25	11.154%	$139.2204	$139.22	$139.20	$139.20
Purchase #3	$122.93	12.348%	$138.1094	$138.11	$138.10	$138.10
Purchase #4	$139.91	8.379%	$151.6331	$151.63	$151.65	$151.60
Purchase #5	$31.89	8.473%	$34.592	$34.59	$34.60	$34.60
Purchase #6	$209.97	11.218%	$233.5244	$233.52	$233.50	$233.50
Purchase #7	$215.86	10.431%	$238.3764	$238.38	$238.40	$238.40
7 purchase totals =	$917.33		$1,012.9476	$1,012.94	$1,012.95	$1,012.90