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	$79.40	4.711%	$83.1405	$83.14	$83.15	$83.10
Purchase #2	$117.72	6.862%	$125.7979	$125.80	$125.80	$125.80
Purchase #3	$32.62	6.161%	$34.6297	$34.63	$34.65	$34.60
Purchase #4	$55.35	7.558%	$59.5334	$59.53	$59.55	$59.50
Purchase #5	$130.53	4.380%	$136.2472	$136.25	$136.25	$136.20
Purchase #6	$68.94	13.144%	$78.0015	$78.00	$78.00	$78.00
Purchase #7	$29.32	5.831%	$31.0296	$31.03	$31.05	$31.00
7 purchase totals =	$513.88		$548.3798	$548.38	$548.45	$548.20