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	$72.42	6.824%	$77.3619	$77.36	$77.35	$77.40
Purchase #2	$113.53	4.454%	$118.5866	$118.59	$118.60	$118.60
Purchase #3	$97.73	8.859%	$106.3879	$106.39	$106.40	$106.40
Purchase #4	$66.60	7.734%	$71.7508	$71.75	$71.75	$71.80
Purchase #5	$11.78	6.582%	$12.5554	$12.56	$12.55	$12.60
Purchase #6	$20.68	6.254%	$21.9733	$21.97	$21.95	$22.00
Purchase #7	$142.31	7.282%	$152.673	$152.67	$152.65	$152.70
7 purchase totals =	$525.05		$561.2889	$561.29	$561.25	$561.50