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	$98.92	5.516%	$104.3764	$104.38	$104.40	$104.40
Purchase #2	$130.54	12.256%	$146.539	$146.54	$146.55	$146.50
Purchase #3	$46.94	4.758%	$49.1734	$49.17	$49.15	$49.20
Purchase #4	$188.90	9.221%	$206.3185	$206.32	$206.30	$206.30
Purchase #5	$94.90	12.211%	$106.4882	$106.49	$106.50	$106.50
Purchase #6	$105.71	10.265%	$116.5611	$116.56	$116.55	$116.60
Purchase #7	$60.81	11.218%	$67.6317	$67.63	$67.65	$67.60
7 purchase totals =	$726.72		$797.0883	$797.09	$797.10	$797.10