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	$138.83	12.393%	$156.0352	$156.04	$156.05	$156.00
Purchase #2	$72.67	8.265%	$78.6762	$78.68	$78.70	$78.70
Purchase #3	$47.36	12.302%	$53.1862	$53.19	$53.20	$53.20
Purchase #4	$52.49	4.558%	$54.8825	$54.88	$54.90	$54.90
Purchase #5	$20.27	9.340%	$22.1632	$22.16	$22.15	$22.20
Purchase #6	$95.62	3.291%	$98.7669	$98.77	$98.75	$98.80
Purchase #7	$36.88	4.434%	$38.5153	$38.52	$38.50	$38.50
7 purchase totals =	$464.12		$502.2255	$502.24	$502.25	$502.30