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	$58.90	10.681%	$65.1911	$65.19	$65.20	$65.20
Purchase #2	$244.63	5.864%	$258.9751	$258.98	$259.00	$259.00
Purchase #3	$69.83	11.499%	$77.8598	$77.86	$77.85	$77.90
Purchase #4	$93.38	6.787%	$99.7177	$99.72	$99.70	$99.70
Purchase #5	$238.27	8.656%	$258.8947	$258.89	$258.90	$258.90
Purchase #6	$49.58	12.124%	$55.5911	$55.59	$55.60	$55.60
Purchase #7	$23.94	13.250%	$27.1121	$27.11	$27.10	$27.10
7 purchase totals =	$778.53		$843.3416	$843.34	$843.35	$843.40