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	$31.48	10.458%	$34.7722	$34.77	$34.75	$34.80
Purchase #2	$99.26	7.285%	$106.4911	$106.49	$106.50	$106.50
Purchase #3	$53.65	10.784%	$59.4356	$59.44	$59.45	$59.40
Purchase #4	$152.89	5.234%	$160.8923	$160.89	$160.90	$160.90
Purchase #5	$95.85	7.714%	$103.2439	$103.24	$103.25	$103.20
Purchase #6	$85.80	3.724%	$88.9952	$89.00	$89.00	$89.00
Purchase #7	$141.28	4.852%	$148.1349	$148.13	$148.15	$148.10
7 purchase totals =	$660.21		$701.9652	$701.96	$702.00	$701.90