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	$244.61	12.236%	$274.5405	$274.54	$274.55	$274.50
Purchase #2	$235.81	7.307%	$253.0406	$253.04	$253.05	$253.00
Purchase #3	$9.80	10.846%	$10.8629	$10.86	$10.85	$10.90
Purchase #4	$47.61	9.799%	$52.2753	$52.28	$52.30	$52.30
Purchase #5	$227.32	8.289%	$246.1626	$246.16	$246.15	$246.20
Purchase #6	$131.53	7.567%	$141.4829	$141.48	$141.50	$141.50
Purchase #7	$39.27	5.738%	$41.5233	$41.52	$41.50	$41.50
7 purchase totals =	$935.95		$1,019.8881	$1,019.88	$1,019.90	$1,019.90