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	$240.75	6.853%	$257.2486	$257.25	$257.25	$257.20
Purchase #2	$201.40	4.466%	$210.3945	$210.39	$210.40	$210.40
Purchase #3	$120.78	10.798%	$133.8218	$133.82	$133.80	$133.80
Purchase #4	$58.41	12.797%	$65.8847	$65.88	$65.90	$65.90
Purchase #5	$66.38	9.665%	$72.7956	$72.80	$72.80	$72.80
Purchase #6	$110.50	5.288%	$116.3432	$116.34	$116.35	$116.30
Purchase #7	$92.82	6.787%	$99.1197	$99.12	$99.10	$99.10
7 purchase totals =	$891.04		$955.6081	$955.60	$955.60	$955.50