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	$36.86	7.242%	$39.5294	$39.53	$39.55	$39.50
Purchase #2	$177.57	4.685%	$185.8892	$185.89	$185.90	$185.90
Purchase #3	$141.88	3.482%	$146.8203	$146.82	$146.80	$146.80
Purchase #4	$217.78	12.240%	$244.4363	$244.44	$244.45	$244.40
Purchase #5	$139.92	3.519%	$144.8438	$144.84	$144.85	$144.80
Purchase #6	$149.46	12.275%	$167.8062	$167.81	$167.80	$167.80
Purchase #7	$52.40	9.772%	$57.5205	$57.52	$57.50	$57.50
7 purchase totals =	$915.87		$986.8457	$986.85	$986.85	$986.70