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	$249.64	4.668%	$261.2932	$261.29	$261.30	$261.30
Purchase #2	$184.98	3.221%	$190.9382	$190.94	$190.95	$190.90
Purchase #3	$105.46	10.164%	$116.179	$116.18	$116.20	$116.20
Purchase #4	$237.89	10.780%	$263.5345	$263.53	$263.55	$263.50
Purchase #5	$9.90	9.635%	$10.8539	$10.85	$10.85	$10.90
Purchase #6	$72.69	5.364%	$76.5891	$76.59	$76.60	$76.60
Purchase #7	$71.63	9.526%	$78.4535	$78.45	$78.45	$78.50
7 purchase totals =	$932.19		$997.8414	$997.83	$997.90	$997.90