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	$136.50	8.319%	$147.8554	$147.86	$147.85	$147.90
Purchase #2	$103.82	7.352%	$111.4528	$111.45	$111.45	$111.50
Purchase #3	$77.91	8.160%	$84.2675	$84.27	$84.25	$84.30
Purchase #4	$232.81	11.841%	$260.377	$260.38	$260.40	$260.40
Purchase #5	$122.54	7.491%	$131.7195	$131.72	$131.70	$131.70
Purchase #6	$25.90	12.663%	$29.1797	$29.18	$29.20	$29.20
Purchase #7	$78.90	7.836%	$85.0826	$85.08	$85.10	$85.10
7 purchase totals =	$778.38		$849.9345	$849.94	$849.95	$850.10