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	$15.62	12.413%	$17.5589	$17.56	$17.55	$17.60
Purchase #2	$196.68	13.744%	$223.7117	$223.71	$223.70	$223.70
Purchase #3	$18.51	13.321%	$20.9757	$20.98	$21.00	$21.00
Purchase #4	$76.86	11.835%	$85.9564	$85.96	$85.95	$86.00
Purchase #5	$156.46	7.679%	$168.4746	$168.47	$168.45	$168.50
Purchase #6	$130.34	11.397%	$145.1948	$145.19	$145.20	$145.20
Purchase #7	$54.89	11.763%	$61.3467	$61.35	$61.35	$61.30
7 purchase totals =	$649.36		$723.2188	$723.22	$723.20	$723.30