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	$20.44	7.198%	$21.9113	$21.91	$21.90	$21.90
Purchase #2	$118.90	10.266%	$131.1063	$131.11	$131.10	$131.10
Purchase #3	$98.41	3.314%	$101.6713	$101.67	$101.65	$101.70
Purchase #4	$20.99	7.382%	$22.5395	$22.54	$22.55	$22.50
Purchase #5	$203.25	6.140%	$215.7296	$215.73	$215.75	$215.70
Purchase #6	$76.67	7.698%	$82.5721	$82.57	$82.55	$82.60
Purchase #7	$44.61	3.296%	$46.0803	$46.08	$46.10	$46.10
7 purchase totals =	$583.27		$621.6104	$621.61	$621.60	$621.60