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	$30.46	5.349%	$32.0893	$32.09	$32.10	$32.10
Purchase #2	$154.53	6.459%	$164.5111	$164.51	$164.50	$164.50
Purchase #3	$219.63	6.671%	$234.2815	$234.28	$234.30	$234.30
Purchase #4	$199.36	9.801%	$218.8993	$218.90	$218.90	$218.90
Purchase #5	$59.61	10.537%	$65.8911	$65.89	$65.90	$65.90
Purchase #6	$127.91	3.756%	$132.7143	$132.71	$132.70	$132.70
Purchase #7	$51.61	5.715%	$54.5595	$54.56	$54.55	$54.60
7 purchase totals =	$843.11		$902.9461	$902.94	$902.95	$903.00