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	$56.71	6.857%	$60.5986	$60.60	$60.60	$60.60
Purchase #2	$191.38	9.671%	$209.8884	$209.89	$209.90	$209.90
Purchase #3	$34.75	10.698%	$38.4676	$38.47	$38.45	$38.50
Purchase #4	$156.88	6.511%	$167.0945	$167.09	$167.10	$167.10
Purchase #5	$172.71	10.140%	$190.2228	$190.22	$190.20	$190.20
Purchase #6	$152.96	6.263%	$162.5399	$162.54	$162.55	$162.50
Purchase #7	$5.61	9.216%	$6.127	$6.13	$6.15	$6.10
7 purchase totals =	$771.00		$834.9388	$834.94	$834.95	$834.90