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	$50.85	3.273%	$52.5143	$52.51	$52.50	$52.50
Purchase #2	$73.86	9.448%	$80.8383	$80.84	$80.85	$80.80
Purchase #3	$196.35	12.659%	$221.2059	$221.21	$221.20	$221.20
Purchase #4	$157.53	6.849%	$168.3192	$168.32	$168.30	$168.30
Purchase #5	$215.38	12.121%	$241.4862	$241.49	$241.50	$241.50
Purchase #6	$202.86	10.613%	$224.3895	$224.39	$224.40	$224.40
Purchase #7	$41.76	4.632%	$43.6943	$43.69	$43.70	$43.70
7 purchase totals =	$938.59		$1,032.4477	$1,032.45	$1,032.45	$1,032.40