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	$234.63	13.325%	$265.8944	$265.89	$265.90	$265.90
Purchase #2	$220.33	10.137%	$242.6649	$242.66	$242.65	$242.70
Purchase #3	$175.85	13.582%	$199.7339	$199.73	$199.75	$199.70
Purchase #4	$25.70	5.705%	$27.1662	$27.17	$27.15	$27.20
Purchase #5	$137.71	3.356%	$142.3315	$142.33	$142.35	$142.30
Purchase #6	$49.79	11.674%	$55.6025	$55.60	$55.60	$55.60
Purchase #7	$112.44	9.595%	$123.2286	$123.23	$123.25	$123.20
7 purchase totals =	$956.45		$1,056.6220	$1,056.61	$1,056.65	$1,056.60