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	$229.90	11.491%	$256.3178	$256.32	$256.30	$256.30
Purchase #2	$130.92	13.223%	$148.2316	$148.23	$148.25	$148.20
Purchase #3	$78.39	10.196%	$86.3826	$86.38	$86.40	$86.40
Purchase #4	$25.42	8.334%	$27.5385	$27.54	$27.55	$27.50
Purchase #5	$160.29	6.343%	$170.4572	$170.46	$170.45	$170.50
Purchase #6	$144.96	5.785%	$153.3459	$153.35	$153.35	$153.30
Purchase #7	$16.98	12.591%	$19.118	$19.12	$19.10	$19.10
7 purchase totals =	$786.86		$861.3916	$861.40	$861.40	$861.30