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	$158.53	3.753%	$164.4796	$164.48	$164.50	$164.50
Purchase #2	$37.44	4.437%	$39.1012	$39.10	$39.10	$39.10
Purchase #3	$118.85	9.488%	$130.1265	$130.13	$130.15	$130.10
Purchase #4	$223.51	13.742%	$254.2247	$254.22	$254.20	$254.20
Purchase #5	$27.96	12.806%	$31.5406	$31.54	$31.55	$31.50
Purchase #6	$21.65	11.357%	$24.1088	$24.11	$24.10	$24.10
Purchase #7	$100.60	12.453%	$113.1277	$113.13	$113.15	$113.10
7 purchase totals =	$688.54		$756.7091	$756.71	$756.75	$756.60