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	$6.89	7.133%	$7.3815	$7.38	$7.40	$7.40
Purchase #2	$169.95	6.448%	$180.9084	$180.91	$180.90	$180.90
Purchase #3	$47.73	10.404%	$52.6958	$52.70	$52.70	$52.70
Purchase #4	$152.79	9.655%	$167.5419	$167.54	$167.55	$167.50
Purchase #5	$54.25	13.643%	$61.6513	$61.65	$61.65	$61.70
Purchase #6	$60.47	3.518%	$62.5973	$62.60	$62.60	$62.60
Purchase #7	$31.98	6.356%	$34.0126	$34.01	$34.00	$34.00
7 purchase totals =	$524.06		$566.7888	$566.79	$566.80	$566.80