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	$116.26	13.144%	$131.5412	$131.54	$131.55	$131.50
Purchase #2	$245.87	7.653%	$264.6864	$264.69	$264.70	$264.70
Purchase #3	$205.81	8.665%	$223.6434	$223.64	$223.65	$223.60
Purchase #4	$27.51	13.454%	$31.2112	$31.21	$31.20	$31.20
Purchase #5	$217.34	6.233%	$230.8868	$230.89	$230.90	$230.90
Purchase #6	$30.77	5.549%	$32.4774	$32.48	$32.50	$32.50
Purchase #7	$48.45	6.844%	$51.7659	$51.77	$51.75	$51.80
7 purchase totals =	$892.01		$966.2123	$966.22	$966.25	$966.20