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	$116.97	6.239%	$124.2678	$124.27	$124.25	$124.30
Purchase #2	$98.74	4.201%	$102.8881	$102.89	$102.90	$102.90
Purchase #3	$92.90	10.366%	$102.53	$102.53	$102.55	$102.50
Purchase #4	$90.78	9.712%	$99.5966	$99.60	$99.60	$99.60
Purchase #5	$237.28	9.473%	$259.7575	$259.76	$259.75	$259.80
Purchase #6	$96.62	4.792%	$101.25	$101.25	$101.25	$101.30
Purchase #7	$123.91	12.684%	$139.6267	$139.63	$139.65	$139.60
7 purchase totals =	$857.20		$929.9167	$929.93	$929.95	$930.00