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	$28.42	11.502%	$31.6889	$31.69	$31.70	$31.70
Purchase #2	$132.68	12.558%	$149.342	$149.34	$149.35	$149.30
Purchase #3	$69.53	12.711%	$78.368	$78.37	$78.35	$78.40
Purchase #4	$100.39	11.427%	$111.8616	$111.86	$111.85	$111.90
Purchase #5	$148.75	7.725%	$160.2409	$160.24	$160.25	$160.20
Purchase #6	$69.42	5.792%	$73.4408	$73.44	$73.45	$73.40
Purchase #7	$39.95	3.163%	$41.2136	$41.21	$41.20	$41.20
7 purchase totals =	$589.14		$646.1558	$646.15	$646.15	$646.10