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	$141.31	6.507%	$150.505	$150.51	$150.50	$150.50
Purchase #2	$179.64	8.421%	$194.7675	$194.77	$194.75	$194.80
Purchase #3	$17.36	3.171%	$17.9105	$17.91	$17.90	$17.90
Purchase #4	$218.66	5.815%	$231.3751	$231.38	$231.40	$231.40
Purchase #5	$94.77	11.697%	$105.8552	$105.86	$105.85	$105.90
Purchase #6	$35.86	12.225%	$40.2439	$40.24	$40.25	$40.20
Purchase #7	$153.46	8.273%	$166.1557	$166.16	$166.15	$166.20
7 purchase totals =	$841.06		$906.8129	$906.83	$906.80	$906.90