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	$35.50	5.405%	$37.4188	$37.42	$37.40	$37.40
Purchase #2	$139.87	11.634%	$156.1425	$156.14	$156.15	$156.10
Purchase #3	$86.43	13.669%	$98.2441	$98.24	$98.25	$98.20
Purchase #4	$221.61	13.459%	$251.4365	$251.44	$251.45	$251.40
Purchase #5	$80.83	11.458%	$90.0915	$90.09	$90.10	$90.10
Purchase #6	$139.87	12.326%	$157.1104	$157.11	$157.10	$157.10
Purchase #7	$187.55	4.506%	$196.001	$196.00	$196.00	$196.00
7 purchase totals =	$891.66		$986.4448	$986.44	$986.45	$986.30