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	$59.73	11.376%	$66.5249	$66.52	$66.50	$66.50
Purchase #2	$187.95	12.396%	$211.2483	$211.25	$211.25	$211.20
Purchase #3	$245.68	5.654%	$259.5707	$259.57	$259.55	$259.60
Purchase #4	$83.55	3.266%	$86.2787	$86.28	$86.30	$86.30
Purchase #5	$83.48	6.872%	$89.2167	$89.22	$89.20	$89.20
Purchase #6	$129.55	7.121%	$138.7753	$138.78	$138.80	$138.80
Purchase #7	$138.82	12.469%	$156.1295	$156.13	$156.15	$156.10
7 purchase totals =	$928.76		$1,007.7441	$1,007.75	$1,007.75	$1,007.70