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	$229.96	6.513%	$244.9373	$244.94	$244.95	$244.90
Purchase #2	$127.56	13.523%	$144.8099	$144.81	$144.80	$144.80
Purchase #3	$101.31	12.791%	$114.2686	$114.27	$114.25	$114.30
Purchase #4	$78.36	6.540%	$83.4847	$83.48	$83.50	$83.50
Purchase #5	$102.84	5.864%	$108.8705	$108.87	$108.85	$108.90
Purchase #6	$179.40	3.499%	$185.6772	$185.68	$185.70	$185.70
Purchase #7	$84.88	13.693%	$96.5026	$96.50	$96.50	$96.50
7 purchase totals =	$904.31		$978.5508	$978.55	$978.55	$978.60