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	$74.86	7.512%	$80.4835	$80.48	$80.50	$80.50
Purchase #2	$231.50	11.269%	$257.5877	$257.59	$257.60	$257.60
Purchase #3	$179.71	9.370%	$196.5488	$196.55	$196.55	$196.50
Purchase #4	$118.94	7.550%	$127.92	$127.92	$127.90	$127.90
Purchase #5	$74.52	7.277%	$79.9428	$79.94	$79.95	$79.90
Purchase #6	$222.96	6.854%	$238.2417	$238.24	$238.25	$238.20
Purchase #7	$58.56	4.591%	$61.2485	$61.25	$61.25	$61.20
7 purchase totals =	$961.05		$1,041.9730	$1,041.97	$1,042.00	$1,041.80