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	$112.43	13.253%	$127.3303	$127.33	$127.35	$127.30
Purchase #2	$63.61	10.279%	$70.1485	$70.15	$70.15	$70.10
Purchase #3	$79.72	13.632%	$90.5874	$90.59	$90.60	$90.60
Purchase #4	$79.82	5.400%	$84.1303	$84.13	$84.15	$84.10
Purchase #5	$243.30	7.657%	$261.9295	$261.93	$261.95	$261.90
Purchase #6	$194.36	7.402%	$208.7465	$208.75	$208.75	$208.70
Purchase #7	$54.81	3.207%	$56.5678	$56.57	$56.55	$56.60
7 purchase totals =	$828.05		$899.4403	$899.45	$899.50	$899.30