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	$245.46	11.338%	$273.2903	$273.29	$273.30	$273.30
Purchase #2	$28.71	3.870%	$29.8211	$29.82	$29.80	$29.80
Purchase #3	$53.27	10.730%	$58.9859	$58.99	$59.00	$59.00
Purchase #4	$180.38	8.389%	$195.5121	$195.51	$195.50	$195.50
Purchase #5	$134.54	12.387%	$151.2055	$151.21	$151.20	$151.20
Purchase #6	$128.76	12.437%	$144.7739	$144.77	$144.75	$144.80
Purchase #7	$66.79	9.106%	$72.8719	$72.87	$72.85	$72.90
7 purchase totals =	$837.91		$926.4607	$926.46	$926.40	$926.50