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	$18.84	10.272%	$20.7752	$20.78	$20.80	$20.80
Purchase #2	$124.63	6.503%	$132.7347	$132.73	$132.75	$132.70
Purchase #3	$187.83	6.817%	$200.6344	$200.63	$200.65	$200.60
Purchase #4	$199.83	11.365%	$222.5407	$222.54	$222.55	$222.50
Purchase #5	$80.96	13.251%	$91.688	$91.69	$91.70	$91.70
Purchase #6	$210.76	6.696%	$224.8725	$224.87	$224.85	$224.90
Purchase #7	$156.84	12.758%	$176.8496	$176.85	$176.85	$176.80
7 purchase totals =	$979.69		$1,070.0951	$1,070.09	$1,070.15	$1,070.00