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	$137.25	12.519%	$154.4323	$154.43	$154.45	$154.40
Purchase #2	$13.71	10.239%	$15.1138	$15.11	$15.10	$15.10
Purchase #3	$79.79	12.241%	$89.5571	$89.56	$89.55	$89.60
Purchase #4	$64.38	12.600%	$72.4919	$72.49	$72.50	$72.50
Purchase #5	$234.59	9.266%	$256.3271	$256.33	$256.35	$256.30
Purchase #6	$6.56	4.749%	$6.8715	$6.87	$6.85	$6.90
Purchase #7	$84.46	5.336%	$88.9668	$88.97	$88.95	$89.00
7 purchase totals =	$620.74		$683.7605	$683.76	$683.75	$683.80