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	$26.28	10.727%	$29.0991	$29.10	$29.10	$29.10
Purchase #2	$140.83	11.411%	$156.9001	$156.90	$156.90	$156.90
Purchase #3	$13.86	6.609%	$14.776	$14.78	$14.80	$14.80
Purchase #4	$131.75	12.464%	$148.1713	$148.17	$148.15	$148.20
Purchase #5	$88.64	13.156%	$100.3015	$100.30	$100.30	$100.30
Purchase #6	$250.59	3.608%	$259.6313	$259.63	$259.65	$259.60
Purchase #7	$205.43	8.195%	$222.265	$222.27	$222.25	$222.30
7 purchase totals =	$857.38		$931.1443	$931.15	$931.15	$931.20