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	$172.60	10.240%	$190.2742	$190.27	$190.25	$190.30
Purchase #2	$241.44	9.484%	$264.3382	$264.34	$264.35	$264.30
Purchase #3	$144.72	7.134%	$155.0443	$155.04	$155.05	$155.00
Purchase #4	$12.97	7.543%	$13.9483	$13.95	$13.95	$13.90
Purchase #5	$122.50	3.122%	$126.3245	$126.32	$126.30	$126.30
Purchase #6	$170.46	6.419%	$181.4018	$181.40	$181.40	$181.40
Purchase #7	$36.43	11.689%	$40.6883	$40.69	$40.70	$40.70
7 purchase totals =	$901.12		$972.0196	$972.01	$972.00	$971.90