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	$194.46	13.727%	$221.1535	$221.15	$221.15	$221.20
Purchase #2	$72.76	8.463%	$78.9177	$78.92	$78.90	$78.90
Purchase #3	$56.30	5.664%	$59.4888	$59.49	$59.50	$59.50
Purchase #4	$44.32	4.693%	$46.3999	$46.40	$46.40	$46.40
Purchase #5	$138.86	11.539%	$154.8831	$154.88	$154.90	$154.90
Purchase #6	$133.41	9.542%	$146.14	$146.14	$146.15	$146.10
Purchase #7	$246.76	9.592%	$270.4292	$270.43	$270.45	$270.40
7 purchase totals =	$886.87		$977.4122	$977.41	$977.45	$977.40