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	$150.93	9.849%	$165.7951	$165.80	$165.80	$165.80
Purchase #2	$36.65	4.636%	$38.3491	$38.35	$38.35	$38.30
Purchase #3	$76.87	10.828%	$85.1935	$85.19	$85.20	$85.20
Purchase #4	$227.80	4.799%	$238.7321	$238.73	$238.75	$238.70
Purchase #5	$33.59	10.706%	$37.1861	$37.19	$37.20	$37.20
Purchase #6	$79.35	7.842%	$85.5726	$85.57	$85.55	$85.60
Purchase #7	$87.71	12.399%	$98.5852	$98.59	$98.60	$98.60
7 purchase totals =	$692.90		$749.4137	$749.42	$749.45	$749.40