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	$150.77	13.584%	$171.2506	$171.25	$171.25	$171.30
Purchase #2	$175.86	11.348%	$195.8166	$195.82	$195.80	$195.80
Purchase #3	$116.51	6.635%	$124.2404	$124.24	$124.25	$124.20
Purchase #4	$70.60	10.520%	$78.0271	$78.03	$78.05	$78.00
Purchase #5	$36.94	6.458%	$39.3256	$39.33	$39.35	$39.30
Purchase #6	$172.68	8.241%	$186.9106	$186.91	$186.90	$186.90
Purchase #7	$109.69	3.814%	$113.8736	$113.87	$113.85	$113.90
7 purchase totals =	$833.05		$909.4445	$909.45	$909.45	$909.40