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	$35.82	6.402%	$38.1132	$38.11	$38.10	$38.10
Purchase #2	$106.48	11.304%	$118.5165	$118.52	$118.50	$118.50
Purchase #3	$92.40	13.578%	$104.9461	$104.95	$104.95	$104.90
Purchase #4	$215.35	10.514%	$237.9919	$237.99	$238.00	$238.00
Purchase #5	$95.69	10.310%	$105.5556	$105.56	$105.55	$105.60
Purchase #6	$103.48	12.606%	$116.5247	$116.52	$116.50	$116.50
Purchase #7	$111.76	4.853%	$117.1837	$117.18	$117.20	$117.20
7 purchase totals =	$760.98		$838.8317	$838.83	$838.80	$838.80