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	$123.76	12.381%	$139.0827	$139.08	$139.10	$139.10
Purchase #2	$46.47	13.506%	$52.7462	$52.75	$52.75	$52.70
Purchase #3	$134.92	5.776%	$142.713	$142.71	$142.70	$142.70
Purchase #4	$193.43	12.513%	$217.6339	$217.63	$217.65	$217.60
Purchase #5	$120.85	12.816%	$136.3381	$136.34	$136.35	$136.30
Purchase #6	$173.56	9.163%	$189.4633	$189.46	$189.45	$189.50
Purchase #7	$179.25	9.441%	$196.173	$196.17	$196.15	$196.20
7 purchase totals =	$972.24		$1,074.1502	$1,074.14	$1,074.15	$1,074.10