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	$80.89	5.609%	$85.4271	$85.43	$85.45	$85.40
Purchase #2	$173.34	9.572%	$189.9321	$189.93	$189.95	$189.90
Purchase #3	$162.81	5.744%	$172.1618	$172.16	$172.15	$172.20
Purchase #4	$211.33	7.672%	$227.5432	$227.54	$227.55	$227.50
Purchase #5	$235.40	13.224%	$266.5293	$266.53	$266.55	$266.50
Purchase #6	$178.46	4.353%	$186.2284	$186.23	$186.25	$186.20
Purchase #7	$109.68	4.277%	$114.371	$114.37	$114.35	$114.40
7 purchase totals =	$1,151.91		$1,242.1929	$1,242.19	$1,242.25	$1,242.10