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	$90.80	12.823%	$102.4433	$102.44	$102.45	$102.40
Purchase #2	$153.39	3.157%	$158.2325	$158.23	$158.25	$158.20
Purchase #3	$81.55	9.801%	$89.5427	$89.54	$89.55	$89.50
Purchase #4	$68.94	5.547%	$72.7641	$72.76	$72.75	$72.80
Purchase #5	$143.72	9.542%	$157.4338	$157.43	$157.45	$157.40
Purchase #6	$92.90	6.778%	$99.1968	$99.20	$99.20	$99.20
Purchase #7	$106.57	3.225%	$110.0069	$110.01	$110.00	$110.00
7 purchase totals =	$737.87		$789.6201	$789.61	$789.65	$789.50