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	$12.53	3.252%	$12.9375	$12.94	$12.95	$12.90
Purchase #2	$161.43	4.611%	$168.8735	$168.87	$168.85	$168.90
Purchase #3	$167.56	6.373%	$178.2386	$178.24	$178.25	$178.20
Purchase #4	$118.65	6.336%	$126.1677	$126.17	$126.15	$126.20
Purchase #5	$215.57	4.617%	$225.5229	$225.52	$225.50	$225.50
Purchase #6	$109.27	9.574%	$119.7315	$119.73	$119.75	$119.70
Purchase #7	$186.71	11.519%	$208.2171	$208.22	$208.20	$208.20
7 purchase totals =	$971.72		$1,039.6888	$1,039.69	$1,039.65	$1,039.60