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	$136.56	4.356%	$142.5086	$142.51	$142.50	$142.50
Purchase #2	$51.36	12.424%	$57.741	$57.74	$57.75	$57.70
Purchase #3	$128.61	13.660%	$146.1781	$146.18	$146.20	$146.20
Purchase #4	$32.33	13.399%	$36.6619	$36.66	$36.65	$36.70
Purchase #5	$127.33	13.830%	$144.9397	$144.94	$144.95	$144.90
Purchase #6	$113.89	3.123%	$117.4468	$117.45	$117.45	$117.40
Purchase #7	$109.86	4.293%	$114.5763	$114.58	$114.60	$114.60
7 purchase totals =	$699.94		$760.0524	$760.06	$760.10	$760.00