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	$105.33	9.104%	$114.9192	$114.92	$114.90	$114.90
Purchase #2	$250.30	4.155%	$260.7	$260.70	$260.70	$260.70
Purchase #3	$131.98	9.408%	$144.3967	$144.40	$144.40	$144.40
Purchase #4	$82.55	11.738%	$92.2397	$92.24	$92.25	$92.20
Purchase #5	$137.75	7.305%	$147.8126	$147.81	$147.80	$147.80
Purchase #6	$80.59	6.548%	$85.867	$85.87	$85.85	$85.90
Purchase #7	$103.50	7.540%	$111.3039	$111.30	$111.30	$111.30
7 purchase totals =	$892.00		$957.2391	$957.24	$957.20	$957.20