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	$57.54	3.659%	$59.6454	$59.65	$59.65	$59.60
Purchase #2	$59.79	9.305%	$65.3535	$65.35	$65.35	$65.40
Purchase #3	$203.78	8.666%	$221.4396	$221.44	$221.45	$221.40
Purchase #4	$33.89	13.251%	$38.3808	$38.38	$38.40	$38.40
Purchase #5	$231.38	3.459%	$239.3834	$239.38	$239.40	$239.40
Purchase #6	$27.72	3.504%	$28.6913	$28.69	$28.70	$28.70
Purchase #7	$221.58	7.345%	$237.8551	$237.86	$237.85	$237.90
7 purchase totals =	$835.68		$890.7491	$890.75	$890.80	$890.80