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	$76.86	12.290%	$86.3061	$86.31	$86.30	$86.30
Purchase #2	$99.43	7.840%	$107.2253	$107.23	$107.25	$107.20
Purchase #3	$156.65	5.286%	$164.9305	$164.93	$164.95	$164.90
Purchase #4	$164.53	11.502%	$183.4542	$183.45	$183.45	$183.50
Purchase #5	$181.44	13.430%	$205.8074	$205.81	$205.80	$205.80
Purchase #6	$156.27	10.378%	$172.4877	$172.49	$172.50	$172.50
Purchase #7	$183.90	4.213%	$191.6477	$191.65	$191.65	$191.60
7 purchase totals =	$1,019.08		$1,111.8589	$1,111.87	$1,111.90	$1,111.80