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	$104.51	12.407%	$117.4766	$117.48	$117.50	$117.50
Purchase #2	$63.56	4.746%	$66.5766	$66.58	$66.60	$66.60
Purchase #3	$84.61	6.288%	$89.9303	$89.93	$89.95	$89.90
Purchase #4	$31.27	7.602%	$33.6471	$33.65	$33.65	$33.60
Purchase #5	$109.65	13.332%	$124.2685	$124.27	$124.25	$124.30
Purchase #6	$7.93	6.564%	$8.4505	$8.45	$8.45	$8.50
Purchase #7	$208.34	6.755%	$222.4134	$222.41	$222.40	$222.40
7 purchase totals =	$609.87		$662.7630	$662.77	$662.80	$662.80