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	$20.88	5.156%	$21.9566	$21.96	$21.95	$22.00
Purchase #2	$6.75	7.178%	$7.2345	$7.23	$7.25	$7.20
Purchase #3	$38.84	4.863%	$40.7288	$40.73	$40.75	$40.70
Purchase #4	$200.31	6.768%	$213.867	$213.87	$213.85	$213.90
Purchase #5	$41.64	8.839%	$45.3206	$45.32	$45.30	$45.30
Purchase #6	$159.82	7.297%	$171.4821	$171.48	$171.50	$171.50
Purchase #7	$44.75	11.486%	$49.89	$49.89	$49.90	$49.90
7 purchase totals =	$512.99		$550.4796	$550.48	$550.50	$550.50