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	$221.95	9.349%	$242.7001	$242.70	$242.70	$242.70
Purchase #2	$79.32	11.434%	$88.3894	$88.39	$88.40	$88.40
Purchase #3	$52.68	7.373%	$56.5641	$56.56	$56.55	$56.60
Purchase #4	$230.83	6.360%	$245.5108	$245.51	$245.50	$245.50
Purchase #5	$142.50	11.511%	$158.9032	$158.90	$158.90	$158.90
Purchase #6	$38.85	12.872%	$43.8508	$43.85	$43.85	$43.90
Purchase #7	$38.52	8.533%	$41.8069	$41.81	$41.80	$41.80
7 purchase totals =	$804.65		$877.7253	$877.72	$877.70	$877.80