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	$24.89	7.554%	$26.7702	$26.77	$26.75	$26.80
Purchase #2	$8.88	6.800%	$9.4838	$9.48	$9.50	$9.50
Purchase #3	$160.69	7.310%	$172.4364	$172.44	$172.45	$172.40
Purchase #4	$69.73	10.156%	$76.8118	$76.81	$76.80	$76.80
Purchase #5	$6.78	11.334%	$7.5484	$7.55	$7.55	$7.50
Purchase #6	$188.50	4.448%	$196.8845	$196.88	$196.90	$196.90
Purchase #7	$188.42	5.865%	$199.4708	$199.47	$199.45	$199.50
7 purchase totals =	$647.89		$689.4059	$689.40	$689.40	$689.40