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	$75.39	7.582%	$81.1061	$81.11	$81.10	$81.10
Purchase #2	$169.98	5.609%	$179.5142	$179.51	$179.50	$179.50
Purchase #3	$62.67	4.224%	$65.3172	$65.32	$65.30	$65.30
Purchase #4	$100.45	4.307%	$104.7764	$104.78	$104.80	$104.80
Purchase #5	$5.89	3.870%	$6.1179	$6.12	$6.10	$6.10
Purchase #6	$104.74	11.215%	$116.4866	$116.49	$116.50	$116.50
Purchase #7	$58.30	9.873%	$64.056	$64.06	$64.05	$64.10
7 purchase totals =	$577.42		$617.3744	$617.39	$617.35	$617.40