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	$116.30	12.714%	$131.0864	$131.09	$131.10	$131.10
Purchase #2	$156.91	11.107%	$174.338	$174.34	$174.35	$174.30
Purchase #3	$20.82	8.589%	$22.6082	$22.61	$22.60	$22.60
Purchase #4	$158.64	9.407%	$173.5633	$173.56	$173.55	$173.60
Purchase #5	$106.63	4.520%	$111.4497	$111.45	$111.45	$111.40
Purchase #6	$59.86	4.571%	$62.5962	$62.60	$62.60	$62.60
Purchase #7	$106.69	13.299%	$120.8787	$120.88	$120.90	$120.90
7 purchase totals =	$725.85		$796.5205	$796.53	$796.55	$796.50