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	$55.96	4.459%	$58.4553	$58.46	$58.45	$58.50
Purchase #2	$174.69	12.488%	$196.5053	$196.51	$196.50	$196.50
Purchase #3	$95.52	5.350%	$100.6303	$100.63	$100.65	$100.60
Purchase #4	$148.33	10.692%	$164.1894	$164.19	$164.20	$164.20
Purchase #5	$249.41	11.389%	$277.8153	$277.82	$277.80	$277.80
Purchase #6	$152.41	6.246%	$161.9295	$161.93	$161.95	$161.90
Purchase #7	$80.28	10.286%	$88.5376	$88.54	$88.55	$88.50
7 purchase totals =	$956.60		$1,048.0627	$1,048.08	$1,048.10	$1,048.00