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	$246.50	13.675%	$280.2089	$280.21	$280.20	$280.20
Purchase #2	$25.96	12.164%	$29.1178	$29.12	$29.10	$29.10
Purchase #3	$199.81	13.205%	$226.1949	$226.19	$226.20	$226.20
Purchase #4	$159.39	5.165%	$167.6225	$167.62	$167.60	$167.60
Purchase #5	$80.48	11.395%	$89.6507	$89.65	$89.65	$89.70
Purchase #6	$243.98	13.178%	$276.1317	$276.13	$276.15	$276.10
Purchase #7	$28.83	12.339%	$32.3873	$32.39	$32.40	$32.40
7 purchase totals =	$984.95		$1,101.3138	$1,101.31	$1,101.30	$1,101.30