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	$123.52	12.819%	$139.354	$139.35	$139.35	$139.40
Purchase #2	$99.72	9.345%	$109.0388	$109.04	$109.05	$109.00
Purchase #3	$16.75	3.278%	$17.2991	$17.30	$17.30	$17.30
Purchase #4	$115.62	6.463%	$123.0925	$123.09	$123.10	$123.10
Purchase #5	$154.91	6.720%	$165.32	$165.32	$165.30	$165.30
Purchase #6	$117.83	5.524%	$124.3389	$124.34	$124.35	$124.30
Purchase #7	$42.41	6.390%	$45.12	$45.12	$45.10	$45.10
7 purchase totals =	$670.76		$723.5633	$723.56	$723.55	$723.50