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	$76.89	5.770%	$81.3266	$81.33	$81.35	$81.30
Purchase #2	$91.69	7.238%	$98.3265	$98.33	$98.35	$98.30
Purchase #3	$40.43	12.191%	$45.3588	$45.36	$45.35	$45.40
Purchase #4	$130.58	5.215%	$137.3897	$137.39	$137.40	$137.40
Purchase #5	$196.82	11.370%	$219.1984	$219.20	$219.20	$219.20
Purchase #6	$127.74	3.200%	$131.8277	$131.83	$131.85	$131.80
Purchase #7	$84.93	8.458%	$92.1134	$92.11	$92.10	$92.10
7 purchase totals =	$749.08		$805.5411	$805.55	$805.60	$805.50