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	$173.26	3.477%	$179.2843	$179.28	$179.30	$179.30
Purchase #2	$63.94	6.216%	$67.9145	$67.91	$67.90	$67.90
Purchase #3	$95.31	8.840%	$103.7354	$103.74	$103.75	$103.70
Purchase #4	$35.35	10.177%	$38.9476	$38.95	$38.95	$38.90
Purchase #5	$104.29	10.248%	$114.9776	$114.98	$115.00	$115.00
Purchase #6	$206.48	4.859%	$216.5129	$216.51	$216.50	$216.50
Purchase #7	$20.52	6.764%	$21.908	$21.91	$21.90	$21.90
7 purchase totals =	$699.15		$743.2803	$743.28	$743.30	$743.20