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	$127.62	9.661%	$139.9494	$139.95	$139.95	$139.90
Purchase #2	$55.45	12.454%	$62.3557	$62.36	$62.35	$62.40
Purchase #3	$221.52	13.227%	$250.8205	$250.82	$250.80	$250.80
Purchase #4	$50.28	4.316%	$52.4501	$52.45	$52.45	$52.50
Purchase #5	$99.37	13.443%	$112.7283	$112.73	$112.75	$112.70
Purchase #6	$123.86	6.168%	$131.4997	$131.50	$131.50	$131.50
Purchase #7	$201.38	9.677%	$220.8675	$220.87	$220.85	$220.90
7 purchase totals =	$879.48		$970.6712	$970.68	$970.65	$970.70